Online Etymology Dictionary

silly: O.E. gesælig "happy" (related to sæl "happiness"), from W.Gmc. *sæligas (cf. O.N. sæll "happy," Goth. sels "good, kindhearted," O.S. salig, M.Du. salich, O.H.G. salig, Ger. selig "blessed, happy, blissful"), from PIE base *sel- "happy" (cf. Gk. hilaros "gay, cheerful," L. solari "to comfort," salvus "whole, safe"). The word's considerable sense development moved from "blessed" to "pious," to "innocent" (1200), to "harmless," to "pitiable" (c.1280), to "weak" (c.1300), to "feeble in mind, lacking in reason, foolish" (1576). Further tendency toward "stunned, dazed as by a blow" (1886) in knocked silly, etc. Silly season in journalism slang is from 1861 (August and September, when newspapers compensate for a lack of hard news by filling up with trivial stories). Silly Putty trademark claims use from July 1949.
twaddle: "silly talk," 1782, probably from twattle (1556), of obscure origin.
gaga: "crazy, silly," 1905, probably from Fr. gaga "senile, foolish."
potty (adj.): "crazy, silly," 1920, slang, of unknown origin, perhaps connected to potter (v.). Earlier slang senses were "easy to manage" (1899) and "feeble, petty" (1860).
dawdle: c.1656, perhaps a variant of daddle "to walk unsteadily." Perhaps influenced by daw, since the bird was regarded as sluggish and silly. Not in general use until c.1775.
frivolous: 1549, from L. frivolus "silly, empty, trifling, brittle," dim. of *frivos "broken, crumbled," from friare "break, rub away, crumble."
coot: c.1300, cote, used for various water fowl (now limited to Fulica atra and, in North America, F. americana), of uncertain origin (cf. Du. meercoet "lake coot"). Meaning "silly person, fool" is attested from 1766.
oaf: 1610 (implied in oafish), also auf (1621), "a changeling; a foolish child left by the fairies" [Johnson], from a Scand. source, cf. Norw. alfr "silly person," in O.N., "elf" (see elf). Hence, "a misbegotten, deformed idiot." Until recently, some dictionaries still gave the plural as oaves.
fade: c.1320, from O.Fr. fader, from fade "pale, weak, insipid," probably from V.L. *fatidus, some sort of blending of L. fatuus "silly, tasteless" + vapidus "flat, flavorless."
solace (n.): "comfort, consolation," late 13c., from O.Fr. solas, from L. solacium, from solatus, pp. of solari "to console, soothe," from PIE base *sel- "of good mood, to favor" (cf. Gk. hilaros "merry," O.E. gesælig "happy;" see silly). The verb is recorded from c.1300.
nicety: 1366, "folly, stupidity," from O.Fr. niceté "foolishness," from nice "silly" (see nice). Underwent sense evolution parallel to nice, arriving at "minute, subtle point" 1589 and "exactitude" in 1660. Phrase to a nicety "exactly" is attested from 1795.
inane: "silly, empty-headed," 1819, earlier "empty" (1660s), a back-formation of inanity "emptiness, hollowness" (c.1600), later "silliness" (1753), from Fr. inanité, from L. inanitatem "emptiness," from inanis "empty, void, worthless, useless." Inanition is attested from c.1400.
peevish: 1393, peyvesshe "perverse, capricious, silly," of uncertain origin, possibly modeled on L. perversus "reversed, perverse," pp. of pervertere "to turn about" (see pervert). Meaning "cross, fretful" first recorded c.1530. The verb peeve is a 1908 back-formation; pet peeve "the thing that provokes one most" is first attested 1919.
fond: c.1340, originally "foolish, silly," from pt. of fonnen "to fool, be foolish," perhaps from M.E. fonne "fool," of uncertain origin, or related to fun. Meaning evolved by 1590 via "foolishly tender" to "having strong affections for." Another sense of fonne was "to lose savor," which may be the original meaning of the word (e.g. Wyclif: "Gif þe salt be fonnyd it is not worþi," 1380).
badinage: "light railery," 1650s, from Fr. badinage "playfulness, jesting," from badiner (v.) "to jest, joke," from badin "silly, jesting," from O.Prov. badar "to yawn, gape," from L.L. badare "to gape," from *bat-, the root of abash.
pantaloons: 1661, "kind of tights" (originally a Fr. fashion and execrated as such by late 17c. Eng. writers), associated with Pantaloun (1590), silly old man character in It. comedy who wore tight trousers over his skinny legs, from It. Pantalone, originally San Pantaleone, Christian martyr, a popular saint in Venice (Pantaleone in the comedies represents the Venetian). The name is of Gk. origin and means "all-compassionate." Applied to tight long trousers (replacing knee-breeches) by 1798; pants is a shortened form first recorded 1840.
doll: 1560, endearing name for a female pet or a mistress; originally a familiar form of fem. proper name Dorothy (q.v.). The -l- for -r- substitution in nicknames is common in Eng.: cf. Hal for Harold, Moll for Mary, Sally for Sarah, etc. Attested from 1648 as colloquial for "slattern;" sense of "child's toy baby" is c.1700. Transferred back to living beings 1778 in sense of "pretty, silly woman" dolled up is Amer.Eng. 1906. Doll's house first recorded 1783.
sly: c.1200, from O.N. sloegr "cunning, crafty, sly," from P.Gmc. *slogis (cf. Low Ger. slu "cunning, sly"), probably from base *slog- "hit" (see slay), with an original notion of "able to hit." Cf. Ger. verschlagen "cunning, crafty, sly," schlagfertig "quick-witted," lit. "ready to strike," from schlagen "to strike." A non-pejorative use of the word lingered in northern Eng. dialect until 20c. On the sly "in secret" is recorded from 1812. Sly-boots "a seeming Silly, but subtil Fellow" is in the 1700 "Dictionary of the Canting Crew."
feather: O.E. feðer "feather," in pl., "wings," from Gmc. *fethro (cf. O.N. fjöðr, M.Du. vedere, Ger. Feder), from PIE *petra-, zero degree *ptera- "wing, feather," from base *pet- "to rush, to fly" (see petition). To feather one's nest "enrich oneself" is from 1583. Feather-headed "silly" is from 1647. Feather-weight, the lightest allowable, is first recorded 1812, originally in horse-racing; boxing use dates from 1889.
soft: O.E. softe "gentle, easy, comfortable," from W.Gmc. *samfti, from P.Gmc. *samftijaz "level, even, smooth, gentle, soft" (cf. O.S. safti, O.H.G. semfti, Ger. sanft, M.Du. sachte, Du. zacht), from base *som- "fitting, agreeable." Sense of "causing little hardship or suffering" attested from c.1200. Of sounds, from mid-13c. Meaning "foolish, simple, silly" is attested from 1620s. Adjective soft core (in ref. to pornography) is from 1966. Soft rock as a music style is attested from 1969. Soft sell is from 1955. Soft-shoe as a dancing style is attested from 1927. Soft-hearted first recorded 1590s.
vain: c.1300, "devoid of real value, idle, unprofitable," from O.Fr. vein "worthless," from L. vanus "idle, empty," from PIE *wa-no-, from base *eue- "to leave, abandon, give out" (cf. O.E. wanian "to lessen," wan "deficient;" O.N. vanta "to lack;" L. vacare "to be empty," vastus "empty, waste;" Avestan va- "lack," Pers. vang "empty, poor;" Skt. una- "deficient"). Meaning "conceited" first recorded 1692, from earlier sense of "silly, idle, foolish" (1390). Phrase in vain "to no effect" (c.1300, after L. in vanum) preserves the original sense.
happy: mid-14c., "lucky," from hap "chance, fortune" (see haphazard), sense of "very glad" first recorded late 14c. Ousted O.E. eadig (from ead "wealth, riches") and gesælig, which has become silly. O.E. bliðe "happy" survives as blithe. From Greek to Irish, a great majority of the European words for "happy" at first meant "lucky." An exception is Welsh, where the word used first meant "wise." Used in World War II and after as a suffix (e.g. bomb-happy, flak-happy) expressing "dazed or frazzled from stress." Happy hour "early evening period of discount drinks and free hors-d'oeuvres at a bar" is first recorded 1961. Happy-go-lucky is from 1670s. Happy as a clam (1630s) was originally happy as a clam in the mud at high tide, when it can't be dug up and eaten.
nice: late 13c., "foolish, stupid, senseless," from O.Fr. nice "silly, foolish," from L. nescius "ignorant," lit. "not-knowing," from ne- "not" (see un-) + stem of scire "to know." "The sense development has been extraordinary, even for an adj." [Weekley] -- from "timid" (pre-1300); to "fussy, fastidious" (late 14c.); to "dainty, delicate" (c.1400); to "precise, careful" (1500s, preserved in such terms as a nice distinction and nice and early); to "agreeable, delightful" (1769); to "kind, thoughtful" (1830). In 16c.-17c. it is often difficult to determine exactly what is meant when a writer uses this word. By 1926, it was pronounced "too great a favorite with the ladies, who have charmed out of it all its individuality and converted it into a mere diffuser of vague and mild agreeableness." [Fowler]
"I am sure," cried Catherine, "I did not mean to say anything wrong; but it is a nice book, and why should I not call it so?" "Very true," said Henry, "and this is a very nice day, and we are taking a very nice walk; and you are two very nice young ladies. Oh! It is a very nice word indeed! It does for everything." [Jane Austen, "Northanger Abbey"]
pretty: O.E. prættig (W.Saxon), *prettig (Mercian) "cunning, skillful, artful," from prætt, *prett "a trick, wile, craft," from W.Gmc. *pratt- (cf. O.N. prettr "a trick," prettugr "tricky;" Fris. pret, M.Du. perte, Du. pret "trick, joke," Du. prettig "sportive, funny," Flem. pertig "brisk, clever"). Connection between O.E. and M.E. words is uncertain, but if they are the same, meaning had shifted by c.1400 to "manly, gallant," and later moved via "attractive, skillfully made," to "fine," to "beautiful in a slight way" (1440). For sense evolution, compare nice, silly. Used to qualify adjectives and adverbs ("moderately") since 1565. As a verb (usually with up) it is attested from 1916. Prettily is from c.1400; prettify first recorded 1850. Pretty-boy is attested from 1885. A pretty penny "lot of money" is first recorded 1768.
half: O.E. half, halb (Mercian), healf (W. Saxon) "side, part" (original sense preserved in behalf), from P.Gmc. *khalbas "something divided" (cf. O.N. halfr, O.Fris., M.Du. half, Ger. halb, Goth. halbs "half"). Used also in O.E. phrases as in modern Ger., to mean "one half unit less than," cf. þridda healf "two and a half," lit. "half third." The construction in two and a half, etc., is first recorded c.1200. Of time, in half past ten, etc., first attested 1750; in Scottish, the half often is prefixed to the following hour, as in Ger. (halb elf "ten thirty"). Half-and-half "ale and porter" is from 1756; half-baked in sense of "silly" is from 1855; half-breed "mixed race" is from 1760; half-blooded in this sense is from c.1600. Half-brother (early 14c.) and half-sister (c.1200) were in M.E.. Halftime in football is from 1871. half-truth is first recorded 1658; half-hearted is from 1610s. To go off half-cocked "speak or act too hastily" (1833) is in allusion to firearms.