Online Etymology Dictionary

seafaring (adj.): c. 1200, from sea + faring (see fare (v.)).
seafood (n.): "food obtained from the sea," 1836, American English, from sea + food.
seagull (n.): 1540s, from sea + gull (n.).
seal (n.1): "design stamped on wax," especially one attached to a document as evidence of authenticity, c. 1200, from Old French seel "seal on a letter" (Modern French sceau), from Vulgar Latin *sigellum (source of Italian suggello, Spanish sello; also Old Frisian and Middle High German sigel, German Siegel), from Latin sigillum "small picture, engraved figure, seal," diminutive of signum "mark, token" (see sign (n.)). An earlier borrowing directly from Latin is represented by Old English insigel. Technical use, "what prevents the escape of a gas or liquid" is from 1853.
seal (n.2): fish-eating mammal with flippers, Old English seolh "seal," from Proto-Germanic *selkhaz (compare Old Norse selr, Swedish sjöl, Danish sæl, Middle Low German sel, Middle Dutch seel, Old High German selah), of unknown origin, perhaps a borrowing from Finnic. Seal point "dark brown marking on a Siamese cat" is recorded from 1934, from the dark brown color of seal fur; compare seal brown "rich, dark brown color," by 1875. Old English seolhbæð, literally "seal's bath," was an Anglo-Saxon kenning for "the sea."
seal (v.): "to fasten with (or as with) a seal," c. 1200, from seal (n.1). Meaning "to place a seal on (a document)" is recorded from mid-14c.; hence "to conclude, ratify, render official" (late 15c.). Sense of "to close up with wax, lead, cement, etc." is attested from 1660s, from the notion of wax seals on envelopes. In reference to the actions of wood-coatings, 1940. Related: Sealed; sealing. Sealing-wax is attested from c. 1300. To seal (one's) fate (1799) probably reflects the notion of a seal on an execution warrant.
sealant (n.): 1945, from seal (v.) + -ant.
sealskin (n.): early 14c., from seal (n.2) + skin (n.).
seam (n.): Old English seam "seam, suture, junction," from Proto-Germanic *saumaz (source also of Old Frisian sam "hem, seam," Old Norse saumr, Middle Dutch som, Dutch zoom, Old High German soum, German Saum "hem"), from PIE root *syu- "to sew, to bind" (source also of Old English siwian, Latin suere, Sanskrit syuman; see sew).
Chidynge and reproche ... vnsowen the semes of freendshipe in mannes herte. [Chaucer, "Parson's Tale," c. 1386]
Meaning "raised band of stitching on a ball" is recorded from 1888. Geological use is from 1590s.
seam (v.): 1580s, from seam (n.). Related: Seamed; seaming.
seaman (n.): "a sailor," Old English sæmanna (plural); see sea + man (n.). Similar formation in Dutch zeeman, German Seemann, Old Norse sjomaðr.
seamanship (n.): 1766, "acquaintance with the skill of a good seaman," from seaman + -ship.
seamless (adj.): late 15c., from seam + -less. Figurative sense of "whole, integrated" is attested from 1862. Related: Seamlessly; seamlessness.
seamount (n.): by 1908, from sea + mount (n.1).
seamstress (n.): 1640s, with -ess + seamster (also sempster), from Old English seamestre "sewer, tailor, person whose work is sewing," from seam. Originally indicating a woman, but after a while the fem. ending -estre no longer was felt as such and a new one added.
seamy (adj.): c. 1600, "least pleasant, worst," in figurative phrase seamy side, from seam + -y (2); the seamy side of a sewn garment being the less attractive, and thus typically turned in. The popularity of the figurative sense likely is due to its use by Shakespeare in "Othello" IV.ii.146: "Some such Squire he was That turn'd your wits the seamy-side without, And made you to suspect me with the Moore."
Sean: masc. proper name, also Shaun Shawn; Irish form of John.
seance (n.): 1789, "sitting, session," as of a learned society, from French séance "a sitting," from seoir "to sit," from Latin sedere (see sedentary). Meaning "spiritualistic session" first recorded 1845.
seaplane (n.): 1913, from sea + plane (n.2).
seaport (n.): 1590s, from sea + port (n.1).
sear (v.): Old English searian (intransitive) "dry up, to wither," from Proto-Germanic *saurajan (source also of Middle Dutch soor "dry," Old High German soren "become dry"), from root of sear "dried up, withered" (see sere). Meaning "cause to wither" is from early 15c. Meaning "to brand, to burn by hot iron" is recorded from c. 1400, originally especially of cauterizing wounds; figurative use is from 1580s. Related: Seared; searing.
search (v.): c. 1300, from Old French cerchier "to search" (12c., Modern French chercher), from Latin circare "go about, wander, traverse," in Late Latin "to wander hither and thither," from circus "circle" (see circus). Phrase search me as a verbal shrug of ignorance first recorded 1901. Search engine attested from 1988. Search and destroy as a modifier is 1966, American English, from the Vietnam War. Search and rescue is from 1944.
search (n.): c. 1400, "act of searching;" early 15c., "right to investigate illegal activity; examination of records, wills, etc.; a search through an area or a place," from Anglo-French serche, Old French cerche, from cerchier (see search (v.)). Search warrant attested from 1739.
searchable (adj.): 1550s, from search (v.) + -able. Compare unsearchable.
searchlight (n.): also search-light, 1882, from search (v.) + light (n.).
seashell (n.): also sea-shell, Old English sæscel; see sea and shell (n.).
seashore (n.): also sea-shore, 1520s, from sea + shore (n.). Old English used særima "sea-rim," sæ-strande, etc.
seasick (adj.): also sea-sick, 1560s, from sea + sick (n.). Related: Seasickness.
seaside (n.): also sea-side, c. 1200, from sea + side (n.). As an adjective from 1781. Old English had sæhealf.
season (n.): c. 1300, "a period of the year," with reference to weather or work, also "proper time, suitable occasion," from Old French seison, also saison "season, date; right moment, appropriate time" (Modern French saison) "a sowing, planting," from Latin sationem (nominative satio) "a sowing, planting," noun of action from past participle stem of serere "to sow" (see sow (v.)).

Sense shifted in Vulgar Latin from "act of sowing" to "time of sowing," especially "spring, regarded as the chief sowing season." In Old Provençal and Old French (and thus in English), this was extended to "season" in general. In other Indo-European languages, generic "season" (of the year) words typically are from words for "time," sometimes with a word for "year" (as in Latin tempus (anni), German Jahreszeit). Of game (as in out of season) from late 14c. Spanish estacion, Italian stagione are unrelated, being from Latin statio "station."

Meaning "time of year during which a place is most frequented" is from 1705. Season ticket is attested from 1820.
season (v.): "improve the flavor of by adding spices," c. 1300, from Old French assaisoner "to ripen, season," from a- "to" (see ad-) + root of season (n.) on the notion of fruit becoming more palatable as it ripens. Applied to timber by 1540s. In 16c., it also meant "to copulate with."
seasonable (adj.): "suitable as to the time or season," late 14c., from season (n.) + -able. Related: Seasonably; seasonableness.
seasonal (adj.): "pertaining to the seasons; relating to a season," 1829, from season (n.) + -al (1). Of workers or employment, from 1904. Related: Seasonally.
seasoned (adj.): mid-15c., "flavored, spiced," past participle adjective from season (v.). Meaning "fit for use" is from 1540s; that of "acclimatized, accustomed" is from 1640s.
seasoning (n.): "act of adding flavor," 1510s; "something added to a dish to impart flavor," 1570s, verbal noun from season (v.).
seat (n.1): "thing to sit on; act of sitting," c. 1200, from Old Norse sæti "seat, position," from Proto-Germanic *sæt- (source also of Old High German saze, Middle Dutch gesaete "seat," Old High German gisazi, German Gesäß "buttocks"), from PIE root *sed- (1) "to sit" (see sit). Meaning "posterior of the body" (the sitting part) is from c. 1600; sense of "part of a garment which covers the buttocks" is from 1835. Seat belt is from 1915, originally in airplanes.
seat (n.2): "residence, abode, established place," late 13c., extended use of seat (n.1), influenced by Old French siege "seat, established place," and Latin sedes "seat." Meaning "city in which a government sits" is attested from c. 1400. Sense of "right of taking a place in a parliament or other legislative body" is attested from 1774. Old English had sæt "place where one sits in ambush," which also meant "residents, inhabitants," and is the source of the -set in Dorset and Somerset.
seat (v.): 1570s, "to be in a certain position" (implied in seated), from seat (n.2). Of diseases, in the body, from 1610s (hence deep-seated). Meaning "to cause to sit in a seat" is from 1610s, from seat (n.1). Related: Seated; seating.
SEATO: 1954, acronym for Southeast Asia Treaty Organization.
Seattle: city founded 1853, named for Seatlh (c. 1790-1866), native chief who befriended white settlers. His name is in the Salishan tongue.
seavy (adj.): "overgrown with rushes," 1680s, from seave "rush" (c. 1400), from Old Norse sef.
seaweed (n.): 1570s, from sea + weed (n.). An Old English word for it was sæwar; also fleotwyrt ('float-wort').
seaworthy (adj.): 1807, "in fit condition to encounter heavy weather at sea," from sea + worthy. Related: Seaworthiness. Old English had særof "hardy at sea."
sebaceous (adj.): 1728, "secreting sebum," from Latin sebaceus "of tallow," from sebum "tallow, grease" (see sebum). Meaning "oily, greasy, fatty" is from 1783.
Sebastian: masc. proper name, from Latin Sebastianus, from Greek Sebastianos, "man of Sebastia," a city in Pontus that was named for Augustus Caesar, first Roman emperor, from Greek sebastos "venerable," a translation of Latin augustus, the epithet of Caesar.
seborrhea (n.): also seborrhoea, "discharge of sebaceous matter, especially as a scalp condition," 1849, coined in Modern Latin as a hybrid, from sebo-, used as comb. form of Latin sebum "tallow, suet, grease" (see sebum) + Greek hroia "flow, flux," from rhein "to flow" (see rheum)
sebum (n.): secretion of the sebaceous glands, 1728, from medical use of Latin sebum "sebum, suet, grease," probably related to sapo "soap" (see soap (n.)).
sec (n.): 1956, conversational shortening of second (n.).
sec (adj.): of wine, "dry," French sec (10c.), from Latin siccus "dry" (also source of Italian secco); see siccative.
secant (n.): 1590s, from Latin secantem (nominative secans) "a cutting," present participle of secare "to cut" (see section (n.)). First used by Danish mathematician Thomas Fincke in "Geometria Rotundi" (1583).