silly (adj.)

Old English gesælig "happy, fortuitous, prosperous" (related to sæl "happiness"), from Proto-Germanic *sæligas (source also of Old Norse sæll "happy," Old Saxon salig, Middle Dutch salich, Old High German salig, German selig "blessed, happy, blissful," Gothic sels "good, kindhearted").

This is one of the few instances in which an original long e (ee) has become shortened to i. The same change occurs in breeches, and in the American pronunciation of been, with no change in spelling. [Century Dictionary]

The word's considerable sense development moved from "happy" to "blessed" to "pious," to "innocent" (c. 1200), to "harmless," to "pitiable" (late 13c.), "weak" (c. 1300), to "feeble in mind, lacking in reason, foolish" (1570s). 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.

It is a widespread phenomenon that the words for 'innocent', apart from their legal use, develop, through 'harmless, guileless', a disparaging sense 'credulous, naive, simple, foolish.' [Buck]

updated on June 29, 2018

Definitions of silly from WordNet
silly (adj.)
ludicrous, foolish;
a silly idea
Synonyms: goofy / wacky / whacky / zany
silly (adj.)
lacking seriousness; given to frivolity;
silly giggles
Synonyms: airheaded / dizzy / empty-headed / featherbrained / giddy / light-headed / lightheaded
silly (adj.)
inspiring scornful pity; "how silly an ardent and unsuccessful wooer can be especially if he is getting on in years"- Dashiell Hammett;
Synonyms: pathetic / ridiculous
silly (adj.)
dazed from or as if from repeated blows;
knocked silly by the impact
Synonyms: punch-drunk / slaphappy
silly (n.)
a word used for misbehaving children;
don't be a silly
Etymologies are not definitions. From, not affiliated with etymonline.