1.Definition: informal or slang terms for mentally irregular

Related Adjective(s):barmy, bats, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kookie, kooky, loco, loony, loopy, nuts, nutty, whacky

2.Definition: ludicrous, foolish

"Some wacky plan for selling more books"

Related Adjective(s):goofy, silly, whacky, zany