Synonyms For "Whacky" :

1 syllable:

bats, cracked, daft, kookie, nuts

2 syllables:

balmy, barmy, batty, bonkers, buggy, crackers, dotty, fruity, goofy, kooky, loco, loony, loopy, nutty, silly, wacky, zany

3 syllables:

haywire