- probably imitative of the sound of a blow
1 a: to strike with a smart or resounding blow <whack the ball> b: to cut with or as if with a whack :
2chiefly British : to get the better of :
3slang : , intransitive verb: to strike a smart or resounding blow
— whack·er noun
whack. (2008). In Merriam-Webster Online Dictionary.
Retrieved May 15, 2008, from http://www.merriam-webster.com/dictionary/whack