Online Etymology Dictionary

summer (n.1): "hot season of the year," Old English sumor "summer," from Proto-Germanic *sumur- (source also of Old Saxon, Old Norse, Old High German sumar, Old Frisian sumur, Middle Dutch somer, Dutch zomer, German Sommer), from PIE root *sem- (2) "summer" (source also of Sanskrit sama "season, half-year," Avestan hama "in summer," Armenian amarn "summer," Old Irish sam, Old Welsh ham, Welsh haf "summer").

As an adjective from c. 1300. Summer camp as an institution for youth is attested from 1886; summer resort is from 1823; summer school first recorded 1810; theatrical summer stock is attested from 1941 (see stock (n.2)). Old Norse sumarsdag, first day of summer, was the Thursday that fell between April 9 and 15.
summer (n.2): "horizontal bearing beam," late 13c., from Anglo-French sumer, Old French somier "main beam," originally "pack horse," from Vulgar Latin *saumarius, from Late Latin sagmarius "pack horse," from sagma "packsaddle" (see sumpter).
summer (v.): "to pass the summer," mid-15c., from summer (n.1). Related: Summered; summering.
summerize (v.): 1797, "to spend the summer," from summer (n.1) + -ize. From 1935 as "to prepare (something) for summer." Related: Summerized; summerizing.
summerlong (adj.): Old English sumor lang; see summer (n.1) + long (adj.).
summertime (n.): also summer-time, late 14c., somer tyme, from summer (n.1) + time (n.). Earlier were summertide (mid-13c.), sumeres tid (late Old English). In Britain, as two words, with reference to what in U.S. is daylight saving time, recorded from 1916.
summery (adj.): 1812, from summer (n.1) + -y (2).
summit (n.): c. 1400, "highest point, peak," from Middle French somete, from Old French somete "summit, top," diminutive of som, sum "highest part, top of a hill," from Latin summum, neuter of noun use of summus "highest," related to super "over" (see sum (n.)). The meaning "meeting of heads of state" (1950) is from Winston Churchill's metaphor of "a parley at the summit."
summon (v.): c. 1200, "call, send for, ask the presence of," especially "call, cite, or notify by authority to be at a certain place at a certain time" (late 13c.), from Anglo-French sumunre and directly from Old French somonre, variant of sumundre, somondre "summon," from Vulgar Latin *summundre "to call, cite," from Latin summonere "hint to, remind privately," from sub "under" (see sub-) + monere "warn, advise" (see monitor (n.)). In part also from Medieval Latin use of summonere. Meaning "arouse, excite to action" is from 1580s. Related: Summoned; summoning.
summoner (n.): "petty officer who cites persons to appear in court," secular or ecclesiastical, early 14c. (mid-13c. as a surname), from Anglo-French sumenour, Old French somoneor, from Medieval Latin summonitorem, from past participle stem of summonere (see summon). Contracted form sumner is from mid-14c.
summons (n.): "authoritative call to be at a certain place for a certain purpose," late 13c., from Old French sumunse, noun use of fem. past participle of somondre (see summon (v.)). As a verb from 1650s.
summum bonam (n.): Latin, literally "highest good" (in ethics), from Cicero; see summit, bene-. Plural summa bona.
sumo (n.): 1880, from Japanese sumo "to compete."
sump (n.): mid-15c., "marsh, morass" (from mid-13c. in place names), from Middle Dutch somp or Middle Low German sump, from Proto-Germanic *sumpaz, from PIE *swombho- "spongy." Meaning "pit to collect water" is first found 1650s. Sump-pump (1884) originally was in mining.
sumpter (n.): c. 1300, "driver of a pack horse," from Old French sommetier "pack-horse driver," from Vulgar Latin *sagmatarius "a pack horse driver," from Late Latin sagmat- "a pack, burden," stem of sagma "packsaddle," from Greek sagma, probably related to sattein "to pack, press, stuff." Used from mid-15c. of horses and mules for carrying loads.
sumptuary (adj.): "pertaining to expense," c. 1600, from Latin sumptuarius "relating to expenses," from sumptus "expense, cost," from sumere "to spend, consume" (see sumptuous).
sumptuous (adj.): late 15c., from Old French sumptueux or directly from Latin sumptuosus "costly, very expensive; lavish, wasteful," from sumptus, past participle of sumere "to borrow, buy, spend, eat, drink, consume, employ, take, take up," contraction of *sub-emere, from sub- "under" (see sub-) + emere "to take, buy" (see exempt (adj.)). Related: Sumptuously; sumptuousness.
sun (v.): 1510s, "to set something in the sun," from sun (n.). Intransitive meaning "expose oneself to the sun" is recorded from c. 1600. Sun-bathing is attested from c. 1600.
sun (n.): Old English sunne "sun," from Proto-Germanic *sunnon (source also of Old Norse, Old Saxon, Old High German sunna, Middle Dutch sonne, Dutch zon, German Sonne, Gothic sunno "the sun"), from PIE *s(u)wen- (source also of Avestan xueng "sun," Old Irish fur-sunnud "lighting up"), alternative form of root *saewel- "to shine; sun" (see Sol).

Old English sunne was feminine (as generally in Germanic), and the fem. pronoun was used in English until 16c.; since then masc. has prevailed. The empire on which the sun never sets (1630) originally was the Spanish, later the British. To have one's place in the sun (1680s) is from Pascal's "Pensées"; the German imperial foreign policy sense (1897) is from a speech by von Bülow.
sun-dance (n.): Native American ceremony, 1849, from sun (n.) + dance (n.).
sun-dress (n.): also sundress, 1942, from sun (n.) + dress (n.).
sun-dried (adj.): 1630s in reference to vegetable matter, from sun (n.) + past participle adjective from dry (v.).
sun-up (n.): also sunup, "sunrise," 1712, from sun (n.) + up (adv.). In local use in U.S., and, according to OED, also in Caribbean English and formerly in South Africa.
sun-wake (n.): rays of the setting sun reflected on water, 1891, from sun (n.) + wake (n.). Sailors' tradition says a narrow wake means good weather the following day and bad weather follows a broad wake.
sun-worship (n.): 1670s, from sun (n.) + worship (n.). Related: Sun-worshipper (1670s in the religious sense; 1941 as "devotee of sun-tanning").
sunbeam (n.): Old English sunnebeam; see sun (n.) + beam (n.). As "cheerful person" from 1886.
Sunbelt (n.): 1969, with reference to the Southern U.S., from sun (n.) + belt (n.).
sunburn (v.): 1520s, from sun (n.) + burn (v.). Sunburnt (c. 1400) is older than sunburned (c. 1500, sunne y-brent). As a noun from 1650s.
sunburst (n.): 1816, from sun (n.) + burst (n.).
sundae (n.): 1897, American English, thought to be an alteration of Sunday, perhaps re-spelled in deference to religious feelings; but the reason for the name is uncertain; perhaps "ice cream left over from Sunday, on sale later." For a fuller account of the speculations, see H.L. Mencken, "The American Language," Supplement I (1945), pp.376-7.
Sunday (n.): first day of the week, Old English sunnandæg (Northumbrian sunnadæg), literally "day of the sun," from sunnan, oblique case of sunne "sun" (see sun (n.)) + dæg "day" (see day). A Germanic loan-translation of Latin dies solis "day of the sun," which is itself a loan-translation of Greek hemera heliou. Compare Old Saxon sunnun dag, Old Frisian sunnandei, Old Norse sunnundagr, Dutch zondag, German Sonntag "Sunday."

In European Christian cultures outside Germanic often with a name meaning "the Lord's Day" (Latin Dominica). Sunday-school dates from 1783 (originally for secular instruction); Sunday clothes is from 1640s. Sunday driver is from 1925.
sunder (v.): Old English sundrian, syndrian "to sunder, separate, divide," from sundor "separately, apart," from Proto-Germanic *sunder (source also of Old Norse sundr, Old Frisian sunder, Old High German suntar "aside, apart;" German sondern "to separate"), from PIE root *sene- "apart, separated" (source also of Sanskrit sanutar "far away," Avestan hanare "without," Greek ater "without," Latin sine "without," Old Church Slavonic svene "without," Old Irish sain "different"). Related: Sundered; sundering.
sundial (n.): also sun-dial, 1590s, from sun (n.) + dial (n.). Earlier simply dial.
sundog (n.): "mock sun, parhelion," 1650s; the second element is of obscure origin.
sundown (n.): also sun-down, 1610s, from sun (n.) + down (adv.). OED suggests perhaps a shortening of sun-go-down (1590s). Compare sunset.
sundries (n.): "various small things," 1755, plural of sundry (adj.) used as a noun. "[A] comprehensive term used for brevity, especially in accounts" [Century Dictionary].
sundry (adj.): Old English syndrig "separate, apart, special, various, distinct, characteristic," from sundor "separately, apart, asunder" (see sunder) + -y (2). Compare Old High German suntaric, Swedish söndrig "broken, tattered." Meaning "several" is from 1375. As a noun, from mid-13c. with the sense "various ones." Phrase all and sundry is from late 14c.
sunfish (n.): 1620s, from sun (n.) + fish (n.). Used of various species, with reference to round shape or brilliant appearance. Short form sunny is attested from 1835.
sunflower (n.): 1560s, "heliotrope," from sun (n.) + flower (n.). In reference to the Helianthus (introduced to Europe 1510 from America by the Spaniards) it is attested from 1590s, so called from the appearance of the heads.
sung: a past tense and past participle of sing (v.).
sunglasses (n.): glasses with darkened lenses to protect one's eyes while observing the sun, also sun-glasses, 1878, from sun (n.) + glasses. In popular (non-astronomy) use from 1916. Earlier sunglass (1804) meant a burning glass.
sunk: a past tense and past participle of sink (v.).
sunken (adj.): late 14c., past participle adjective from sink (v.).
sunless (adj.): 1580s, from sun (n.) + -less.
sunlight (n.): c. 1200, from sun (n.) + light (n.). Compare Dutch zonlicht, German sonnenlicht.
sunlit (adj.): 1822, from sun (n.) + lit (adj.).
Sunni (n.): 1620s, from Arabic, "adherent of the Sunnah; Muslim who accepts the orthodox tradition as well as the Quran," from Sunna "traditional teachings of Muhammad" (not, like the Quran, committed to writing, but preserved from his lips by his disciples or founded on his actions), literally "way, custom, course, tradition, usage." Related: Sunnite.
sunny (adj.): "full of sun," early 14c., from sun (n.) + -y (2). Compare Dutch zonnig, German sonnig. Figurative sense of "cheerful" is attested from 1540s. Sunny side in reference to optimistic outlook is from 1831. Eggs served sunny side up first attested 1887, in lunch counter slang, in reference to appearance when served.
Young Man (in Park Row coffee-and-cake saloon)--Waiter, I want a beefsteak, unpeeled potatoes, and a couple of eggs fried on one side only!
Waiter (vociferously)--"Slaughter in the pan," "a Murphy with his coat on," an' "two white wings with the sunny side up!" ["Puck," April 27, 1887]
Related: Sunnily; sunniness. As a noun meaning "sunfish" from 1835.
sunrise (n.): mid-15c., from sun (n.) + rise (v.); perhaps it evolved from a Middle English subjunctive, such as before the sun rise. Earlier in same sense were sunrist (mid-14c.); sunrising (mid-13c.). Compare sunset.
sunroof (n.): of a car, by 1957, from sun (n.) + roof (n.). Originally on European models.