whack / (h)wak/ inf. • v. [tr.] strike forcefully with a sharp blow: his attacker whacked him on the head | [intr.] she found a stick to whack at the branches. ∎  murder: he was whacked while sitting in his car.• n. 1. a sharp or resounding blow.2. a try or attempt: we decided to take a whack at spotting the decade's trends.PHRASES: at a (or one) whack at one time: he built twenty houses at one whack.out of whack out of order; not working: all their calculations were out of whack.PHRASAL VERBS: whack off vulgar slang masturbate.DERIVATIVES: whack·er n.

whack vigorous resounding blow. XVIII. First recorded in Sc.; of imit. orig. (perh. alt. of THWACK).
So vb. XVIII.

Whack

a portion or share.

Examples: whack of booty, 1785; of gold, 1790; of prize money, 1805; of the spoils; of troubles.