Example : Don't be a silly.

Example : Wore a goofy hat.
A silly idea.
Some wacky plan for selling more books.

Synonyms : goofy, wacky, whacky, zany

Example : A dizzy blonde.
Light-headed teenagers.
Silly giggles.

Synonyms : airheaded, dizzy, empty-headed, featherbrained, giddy, light-headed, lightheaded

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

Synonyms : pathetic, ridiculous

Example : Knocked silly by the impact.
Slaphappy with exhaustion.
Punch-drunk with love.

Synonyms : punch-drunk, slaphappy