Wack

Substandard or incorrect (derived from 'out of whack'). Anything that looks cheesy or weak. Badly formed letters, incompetent fills, dumb tags, etc.
Found on http://www.graffiti.org/faq/graffiti.glossary.html

Wack

Slang: Not very good -Usage: 'That's wack' - Other terms Shit, waste
Found on http://news.independent.co.uk/uk/this_britain/article1949469.ece

Wack

Wack is slang for a cigar dipped in embalming fluid.
Found on http://www.probertencyclopaedia.com/browse/ZW.HTM

wack

old name for decomposed basalt
Found on http://phrontistery.info/w.html
No exact match found