Silly describes something that can't be taken seriously. You might not mind telling silly jokes, but you don't want to be told a project you've worked hard at is silly.

Silly originally meant “happy,” which gives the sense of children's games or harmless jokes. Later, it came to mean “foolish”: silly ideas are looked down on because they're not very smart. Silly can also mean a state of foolishness brought on in a specific way. Your mother “worried herself silly” when you stayed out late, and promised to “slap you silly” when you got home.

Definitions of silly

adj ludicrous, foolish

“a silly idea”
cockamamie, cockamamy, goofy, sappy, wacky, whacky, zany
devoid of good sense or judgment

adj inspiring scornful pity

“"how silly an ardent and unsuccessful wooer can be especially if he is getting on in years"- Dashiell Hammett”
pathetic, ridiculous
lacking dignity

adj lacking seriousness; given to frivolity

silly giggles”
airheaded, dizzy, empty-headed, featherbrained, giddy, light-headed, lightheaded
not serious in content or attitude or behavior

adj dazed from or as if from repeated blows

“knocked silly by the impact”
punch-drunk, slaphappy
mentally confused; unable to think with clarity or act intelligently

n a word used for misbehaving children

“don't be a silly
Type of:
child, fry, kid, minor, nestling, nipper, shaver, small fry, tiddler, tike, tyke, youngster
a young person of either sex

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