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1. Ludicrous, foolish
   - goofy [informal], silly, wacky, zany
    
2. [slang] Informal or slang term meaning insane, strange, eccentric or stupid
   "it used to drive my husband whacky";
   - balmy [archaic, slang], barmy [slang], bats [slang], batty [slang], bonkers [slang], buggy [N. Amer, slang], cracked [slang], crackers [slang], daft [Brit, slang], dotty [slang], fruity [slang], haywire [slang], kooky [slang], kookie [slang], loco [slang], loony [slang], loopy [slang], nuts [slang], nutty [slang], round the bend [slang], around the bend [slang], wacky [slang], doolally [Brit, slang], dippy [slang], daffy [slang], nutsy [N. Amer, slang], potty [Brit, slang], daft as a brush [Brit, slang], round the twist [Brit, slang], wacko [slang], dumbass [N. Amer, slang], bughouse [N. Amer, slang], cuckoo [slang], mental [slang], barking mad [Brit, slang], barking [Brit, slang]

Derived forms: whackier, whackiest

See also: daft [Brit, informal], dumb, foolish, imbecile, imbecilic, insane, stupid

Encyclopedia: Whacky