whack

Concise Oxford English Dictionary © 2008 Oxford University Press:
whack /wak/ informal

▶verb

• 1 strike forcefully with a sharp blow.

  ■ defeat heavily.

  ■ place or insert roughly or carelessly.

• 2 N. Amer. murder.

• 3 (whack off) vulgar slang masturbate.

▶noun

• 1 a sharp or resounding blow.

• 2 a try or attempt.

• 3 Brit. a specified share of or contribution to something.

  ■ N. Amer. a large quantity or amount.

– phrases
out of whack N. Amer. & Austral./NZ

• 1 not working.

• 2 skewed or awry.

top (or full) whack chiefly Brit. the maximum price or rate.

– derivatives
whacker noun.

– origin C18: imitative, or perh. an alt. of thwack.