thwack

verb (used with object)

1. to strike or beat vigorously with something flat; whack.

noun

2. a sharp blow with something flat.

verb

1. to beat, hit, or flog, esp with something flat

noun

2. 1. a blow with something flat
   2. the sound made by it

interjection

3. an exclamation imitative of this sound

v.“to hit hard with a stick,” 1520s, of echoic origin. Related: Thwacked; thwacking. The noun is recorded from 1580s.