Online Etymology Dictionary

scag (n.): see skag.
scalable (adj.): 1570s, "able to be climbed;" see scale (v.1) + -able. From 1936 as "able to be graded by scale." Related: Scalably; scalability.
scalar (adj.): "resembling a ladder," 1650s, from Latin scalaris "of or pertaining to a ladder," from scalae (plural) "ladder, steps, flight of steps" (see scale (n.2)). Mathematical sense first recorded 1846.
scalawag (n.): also scallawag, "disreputable fellow," 1848, American English, originally in trade union jargon, of uncertain origin; perhaps an alteration (by influence of wag "habitual joker") of Scottish scallag "farm servant, rustic," itself an alteration of Scalloway, one of the Shetland Islands, wit the reference being to little Shetland ponies (an early recorded sense of scalawag was "undersized or worthless animal," 1854). In U.S. history, used from 1862 as a derogatory term for anti-Confederate native white Southerners.
scald (v.): c. 1200, "to be very hot; to afflict painfully with hot liquid or steam," from Old North French escalder "to scald, to scorch" (Old French eschalder "heat, boil up, bubble," Modern French échauder), from Late Latin excaldare "bathe in hot water" (source also of Spanish escaldar, Italian scaldare "heat with hot water"), from Latin ex- "off" (see ex-) + calidus "hot" (see calorie). Related: Scalded; scalding. The noun is c. 1600, from the verb.
scalding (adj.): early 13c., present participle adjective from scald (v.)). Scalding hot recorded from late 14c.
scale (n.1): "skin plates on fish or snakes," c. 1300, from Old French escale "cup, scale, shell pod, husk" (12c., Modern French écale) "scale, husk," from Frankish *skala or some other Germanic source, from Proto-Germanic *skælo "split, divide" (source also of Dutch schaal "a scale, husk," Old High German scala "shell," Gothic skalja "tile," Old English scealu "shell, husk"), from PIE root *(s)kel- (1) "to cut, cleave, split" (source also of Latin culter "knife," scalpere "to cut, scrape;" Old Church Slavonic skolika "mussel, shell," Russian skala "rind, bark," Lithuanian skelti "split," Old English scell "shell," scalu "drinking cup, bowl, scale of a balance").

In reference to humans, as a condition of certain skin diseases, it is attested from c. 1400. As what falls from one's eye when blindness ends (usually figurative), it echoes Acts ix:18 (Latin tanquam squamæ, Greek hosei lepides).
scale (n.2): weighing instrument, early 15c.; earlier "pan of a balance" (late 14c.); earlier still "drinking cup" (c. 1200), from Old Norse skal "bowl, drinking cup," in plural, "weighing scale" from a noun derivative of Proto-Germanic *skæla "split, divide" (source also of Old Norse skel "shell," Old English scealu, Old Saxon skala "a bowl (to drink from)," Old High German scala, German Schale "a bowl, dish, cup," Middle Dutch scale, Dutch schaal "drinking cup, bowl, shell, scale of a balance"), from PIE root *skel- (1) "to cut" (see scale (n.1)).

The connecting sense seems to be of half of a bivalve ("split") shell used as a drinking cup or a pan for weighing. But according to Paulus Diaconus the "drinking cup" sense originated from a supposed custom of making goblets from skulls (see skull). Related: Scales. This, as a name for the zodiac constellation Libra, is attested in English from 1630s.
scale (v.1): "to climb by or as by a ladder," late 14c., from scale (n.) "a ladder," from Latin scala "ladder, flight of stairs," from *scansla, from stem of scandere "to climb" (see scan (v.)). Related: Scaled; scaling.
scale (n.3): "series of registering marks to measure by; marks laid down to determine distance along a line," late 14c., from Latin scala "ladder, staircase" (see scale (v.1)). Meaning "succession or series of steps" is from c. 1600; that of "standard for estimation" (large scale, small scale, etc.) is from 1620s. Musical sense (1590s), and the meaning "proportion of a representation to the actual object" (1660s) are via Italian scala, from Latin scala.
scale (v.2): "remove the scales of (a fish, etc.)," c. 1400, from scale (n.1). Intransitive sense "to come off in scales" is from 1520s. Related: Scaled; scaling.
scale (v.3): "weigh in scales," 1690s, from scale (n.2). Earlier "to compare, estimate" (c. 1600). Meaning "measure or regulate by a scale" is from 1798, from scale (n.3); that of "weigh out in proper quantities" is from 1841. Scale down "reduce proportionately" is attested from 1887. Scale factor is from 1948. Related: Scaled; scaling.
scale-pan (n.): 1830, from scale (n.2) + pan (n.).
scalene (adj.): "having unequal sides," 1680s, from Late Latin scalenus, from Greek skalenos "uneven, unequal, odd (numbered)," as a noun, "triangle with unequal sides," from skallein "chop, hoe," from PIE *(s)kel- (1) "to cut" (see scale (n.1)).
scallion (n.): late 14c., scalun "kind of onion," also "thing of little value," from Anglo-French escalone, Old North French escalogne, or Old French eschaloigne, all from Vulgar Latin *escalonia, from Latin (cæpa) Ascalonia "(onion) from Ascalon," seaport in southwestern Levant (modern Ashkelon in Israel). Cognate with shallot.
scallop (n.): "bivalve mollusk," c. 1400, from Old French escalope "shell (of a nut), carpace," variant of eschalope, probably from a Germanic source (compare Old Norse skalpr "sheath," Middle Dutch schelpe "shell"); see scale (n.1). The shells of the larger species have been used as domestic utensils. Extended 17c. to objects shaped like scallop shells, especially in design and dress. The verb in the cookery sense, "to bake with sauce in a scallop shell-shaped pan," is attested from 1737. Related: Scalloped; scalloping.
scalp (n.): mid-14c., "top of the head (including hair)," presumably from a Scandinavian source (though exact cognates are wanting) related to Old Norse skalli "a bald head," skalpr "sheath, scabbard,"from the source of scale (n.1). French scalpe, German, Danish, Swedish skalp are from English. Meaning "head skin and hair as proof of death or a victory trophy" is from c. 1600.
scalp (v.): "to cut off (someone's) scalp," 1670s, from scalp (n.), originally in reference to North American Indians. For ticket re-selling sense, see scalper. Related: Scalped; scalping. Compare German skalpern, Danish skalpere, Swedish skalpera. French scalper is from Germanic. Similarity to Latin scalpere "to cut, carve" is accidental.
scalpel (n.): 1742, from Latin scalpellum "a surgical knife," diminutive of scalprum "knife, chisel, tool for scraping or cutting," from scalpere "to carve, cut," related to sculpere "to carve," from PIE root *(s)kel- "to cut, cleave" (see scale (n.1)).
scalper (n.): 1650s as a type of surgical instrument; 1760 as "one who removes scalps," agent noun from scalp (v.).

Meaning "person who re-sells tickets at unauthorized prices for a profit," 1869, American English; earliest reference is to theater tickets, but often used late 19c. of brokers who sold unused portions of railway tickets. [Railways charged less per mile for longer-distance tickets; therefore someone travelling from New York to Chicago could buy a ticket all the way to San Francisco, get out at Chicago and sell it to a scalper, and come away with more money than if he had simply bought a ticket to Chicago; the Chicago scalper would hold the ticket till he found someone looking for a ticket to San Francisco, then sell it to him at a slight advance, but for less than the official price.] Perhaps from scalp (v.); scalper was a generic term for "con man, cheater" in late 19c. Or perhaps the connecting sense is the bounty offered for scalps of certain destructive animals (attested in New England from 1703) and sometimes Indians (i.e., having only part of something, but still getting paid). Some, though, see a connection rather to scalpel, the surgical instrument.
scaly (adj.): also scaley, late 14c., from scale (n.1) + -y (2). Related: Scaliness.
scam: 1963, noun and verb, U.S. slang, a carnival term, of unknown origin. Perhaps related to 19c. British slang scamp "cheater, swindler" (see scamp (n.)).
scamp (n.): 1782, "highway robber," probably from dialectal verb scamp "to roam" (1753, perhaps from 16c.), shortened from scamper. Used affectionately in sense "rascal" since 1808.
scamp (v.): "do in a hasty manner," 1837, perhaps from a Scandinavian source (compare Old Norse skemma "to shorten, make shorter," from skammr "short; brief; lately"), or a blend of scant and skimp [Klein], or a back-formation from scamper. Related: Scamped; scamping.
scamper (v.): "to run quickly," 1680s, probably from Flemish schampeeren, frequentative of schampen "run away," from Old North French escamper (Old French eschamper) "to run away, flee, quit the battlefield, escape," from Vulgar Latin *excampare "decamp," literally "leave the field," from Latin ex campo, from ex "out of" (see ex-) + campo, ablative of campus "field" (see campus). A vogue word late 17c. Related: Scampered; scampering. The noun is 1680s, from the verb.
scampi (n.): 1930, plural of Italian scampo "prawn," ultimately from Greek kampe "a bending, a winding," from PIE root *kamp- "to bend" (see campus).
scan (v.): late 14c., "mark off verse in metric feet," from Late Latin scandere "to scan verse," originally, in classical Latin, "to climb, rise, mount" (the connecting notion is of the rising and falling rhythm of poetry), from PIE *skand- "to spring, leap, climb" (source also of Sanskrit skandati "hastens, leaps, jumps;" Greek skandalon "stumbling block;" Middle Irish sescaind "he sprang, jumped," sceinm "a bound, jump").

Missing -d in English is probably from confusion with suffix -ed (see lawn (n.1)). Sense of "look at closely, examine minutely (as one does when counting metrical feet in poetry)" first recorded 1540s. The (opposite) sense of "look over quickly, skim" is first attested 1926. Related: Scanned; scanning.
scan (n.): 1706, "close investigation," from scan (v.). Meaning "act of scanning" is from 1937; sense of "image obtained by scanning" is from 1953.
scandal (n.): 1580s, "discredit caused by irreligious conduct," from Middle French scandale (12c.), from Late Latin scandalum "cause for offense, stumbling block, temptation," from Greek skandalon "a trap or snare laid for an enemy," in New Testament, metaphorically as "a stumbling block, offense;" originally "trap with a springing device," from PIE *skand- "to leap, climb" (see scan (v.); also see slander (n.), which is another form of the same word).

Attested from early 13c., but the modern word likely is a reborrowing. Meaning "malicious gossip," also "shameful action or event" is from 1590s; sense of "person whose conduct is a disgrace" is from 1630s. Scandal sheet "sensational newspaper" is from 1939. Scandal-monger is from 1702.
scandalise (v.): chiefly British English spelling of scandalize. For suffix, see -ize. Related: Scandalised; scandalising.
scandalize (v.): late 15c., from Middle French scandaliser (12c.), from Church Latin scandalizare, from late Greek skandalizein "to make to stumble; tempt; give offense to (someone)," from skandalon (see scandal). Originally "make a public scandal of;" sense of "shock by doing something improper" first recorded 1640s. Dryden and Shakespeare use simple scandal as a verb. Related: Scandalized; scandalizing; scandalization.
scandalous (adj.): late 15c., from French scandaleux, from Medieval Latin scandalosus "scandalous," from Church Latin scandalum (see scandal). Related: Scandalously.
Scandinavia: 1765, from Late Latin Scandinavia, Skandinovia, a mistake for Scadinavia, from a Germanic source (compare Old English Scedenig, Old Norse Skaney "south end of Sweden"), from Proto-Germanic *skadinaujo "Scadia island," first element of uncertain origin, second element from *aujo "thing on the water," from PIE *akwa- "water" (see aqua-). It might truly have been an island when the word was formed; the coastlines of the Baltic Sea has changed dramatically since the end of the Ice Ages.
Scandinavian (adj.): 1784; see Scandinavia + -ian. From 1830 as a noun; 1959 in reference to furniture and decor. In U.S. colloquial use sometimes Scandahoovian (1929), Scandiwegian. Alternative adjective Scandian (1660s) is from Latin Scandia.
scandium (n.): 1879, from Modern Latin Scandia (see Scandinavia) + chemical ending -ium.
scanner (n.): 1550s, "person who examines critically," agent noun from scan (v.). From 1927 as a type of mechanical device, in mid-20c. use especially of radar and medical devices; later of computer accessories.
scansion (n.): 1670s, "action of marking off of verse in metric feet," from Late Latin scansionem (nominative scansio), in classical Latin, "act of climbing," noun of action from past participle stem of scandere "to climb" (see scan (v.)). From 1650s in English in literal sense of "action of climbing up."
scant (adj.): mid-14c., from a Scandinavian source such as Old Norse skamt, neuter of skammr "short, brief," from Proto-Germanic *skamma- (source also of Old English scamm "short," Old High German skemmen "to shorten"), perhaps ultimately "hornless," from PIE *kem- (1) "hornless" (see hind (n.)). Also in Middle English as a noun, "scant supply, scarcity," from Old Norse. As a verb and adverb from mid-15c.
scantily (adv.): 1774; see scanty + -ly (2).
scantling (adj.): 1520s, "measured or prescribed size," altered from scantlon, scantiloun "dimension" (c. 1400), earlier a type of mason's tool for measuring thickness (c. 1300), a shortening of Old French escantillon (Modern French échantillon "sample pattern"), of uncertain origin; perhaps ultimately from Latin scandere "to climb" (see scan (v.)). Sense influenced by scant. Meaning "small wooden beam" is 1660s. Related: Scantlings.
scantly (adv.): late 14c., from scant + -ly (2). OED reports it "exceedingly common from the 15th to the middle of the 17th c.; in the 18th c. it had app. become obsolere; revived in literary use by Scott."
scantness (n.): late 14c., from scant (adj.) + -ness. Chaucer uses scantity.
scanty (adj.): 1650s, "meager, barely sufficient for use;" 1701, "too small, limited in scope," from scant + -y (2). Related: Scantiness (1560s). Scanties (n.) "underwear" (especially for women) attested from 1928.
scape (n.1): "scenery view," 1773, abstracted from landscape (n.); as a comb. element, first attested use is 1796, in prisonscape.
scape (v.): late 13c., shortened form of escape; frequent in prose till late 17c. Related: Scaped (sometimes 15c.-16c. with strong past tense scope); scaping. As a noun from c. 1300.
scape (n.2): "shaft, stem," c. 1600, from Latin scapus "a stalk, shaft," cognate with Greek skapos "staff," skeptron "staff, scepter" (see scepter).
scapegoat (n.): 1530, "goat sent into the wilderness on the Day of Atonement, symbolic bearer of the sins of the people," coined by Tyndale from scape (n.1) + goat to translate Latin caper emissarius, itself a translation in Vulgate of Hebrew 'azazel (Lev. xvi:8,10,26), which was read as 'ez ozel "goat that departs," but which others hold to be the proper name of a devil or demon in Jewish mythology (sometimes identified with Canaanite deity Aziz).

Jerome's reading also was followed by Martin Luther (der ledige Bock), Symmachus (tragos aperkhomenos), and others (compare French bouc émissaire), but the question of who, or what (or even where) is meant by 'azazel is a vexed one. The Revised Version (1884) simply restores Azazel. But the old translation has its modern defenders:
Azazel is an active participle or participial noun, derived ultimately from azal (connected with the Arabic word azala, and meaning removed), but immediately from the reduplicate form of that verb, azazal. The reduplication of the consonants of the root in Hebrew and Arabic gives the force of repetition, so that while azal means removed, azalzal means removed by a repetition of acts. Azalzel or azazel, therefore, means one who removes by a series of acts. ... The interpretation is founded on sound etymological grounds, it suits the context wherever the word occurs, it is consistent with the remaining ceremonial of the Day of Atonement, and it accords with the otherwise known religious beliefs and symbolical practices of the Israelites. [Rev. F. Meyrick, "Leviticus," London, 1882]
Meaning "one who is blamed or punished for the mistakes or sins of others" first recorded 1824; the verb is attested from 1943. Related: Scapegoated; scapegoating. For the formation, compare scapegrace, also scape-gallows "one who deserves hanging."
scapegrace (n.): 1767, from scape (v.) + grace (n.); as if "one who escapes the grace of God." Possibly influenced by scapegoat.
scaphoid (adj.): 1741, from Modern Latin scaphoides "boat-shaped," from Greek skaphoeides, with -oeides (see -oid) + skaphe "light boat, skiff;" also "basin, trough, a bowl;" literally "thing dug or cut out," from PIE *skabh-, from root *(s)kep- "to cut" (see scabies). Related: Scaphoidal (1680s).
scapula (n.): "shoulder blade," 1570s, Modern Latin, from Late Latin scapula "shoulder," from Latin scapulae (plural) "shoulders, shoulder blades," perhaps originally "spades, shovels," on notion of similar shape, but animal shoulder blades might have been used as scraping tools in primitive times, from PIE *skap-, variant of *skep- "to cut, scrape" (see scabies).