v. To strike (someone or something) with a sharp blow; slap.v. Slang To kill deliberately; murder.verb-intransitive. To deal a sharp, resounding blow.n. A sharp, swift blow.n. The sound made by a sharp, swift blow.phrasal-verb. whack off Vulgar Slang To masturbate.idiom. have Informal To try out; attempt.idiom. out of whack Informal Improperly ordered or balanced; not functioning correctly.idiom. whacked out Slang Exhausted.idiom. whacked out Slang Crazy.idiom. whacked out Slang Under the influence of a mind-altering drug.