from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A person regarded as eccentric.
- adj. Very bad: walked out of a really wack movie.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Egregious
- adj. bad (as in not good), inauthentic, of an inferior quality, contemptible, lacking integrity, inauthentic, lame, or strange.
- adj. crazy, mad, insane
- n. An eccentric; an oddball; a weirdo.
Back-formation from wacky.(American Heritage® Dictionary of the English Language, Fourth Edition)
Back-formation from wacky. (Wiktionary)