Silly:

Definition:  absurd, giddy, foolish

Synonyms:  asinine, balmy, brainless, childish, crazy, dippy, dizzy, empty, empty-headed, fatuous, featherbrained, flighty, foolhardy, frivolous, hare-brained, idiotic, ignorant, illogical, immature, imprudent, inane, inappropriate, inconsistent, irrational, irresponsible, ludicrous, meaningless, muddle-headed,  nitwitted, nonsensical, pointless, preposterous, puerile, ridiculous, senseless, sheepheaded, simple, simpleminded, stupid, unintelligent, unreasonable, unwise, vacuous, witless