v. & n. colloq.
v.tr. 1 strike or beat forcefully with a sharp blow. 2 (as whacked adj.) esp. Brit. tired out; exhausted.
n. 1 a sharp or resounding blow. 2 sl. a share. have a whack at sl. attempt. out of whack esp. US sl. out of order; malfunctioning. whacker n. whacking n.
[ imit., or alt. of THWACK ]