Definition of "Silly" :

noun: a word used for misbehaving children

"Don't be a silly."

adjective: dazed from or as if from repeated blows

"Knocked silly by the impact."

adjective: inspiring scornful pity

"How silly an ardent and unsuccessful wooer can be especially if he is getting on in years."

adjective: lacking seriousness; given to frivolity

"Silly giggles."

adjective: ludicrous, foolish

"A silly idea."