Merriam-Webster's Collegiate® Dictionary, 11th Edition
WHACK
I. verb
Etymology: probably imitative of the sound of a blow
Date: 1719
transitive verb
1. to strike with a smart or resounding blow , to cut with or as if with a whack ; chop , to get the better of ; defeat , murder , kill , intransitive verb to strike a smart or resounding blow, whacker noun
II. noun
Date: 1736
1. a smart or resounding blow, a critical attack, portion , share , condition , state ,
4. an opportunity or attempt to do something , a single action or occasion