wack·o (wāk'ō) n.
pl.wack·os also whack·osSlang A person regarded as eccentric or irrational: "a catchy pop portrait of a wacko who talks to himself in French"(Phoebe Hoban). adj. Wacky.
[Alteration of wacky.]
whack·o (hwāk'ō, wāk'ō) n.
Slang Variant of wacko.