thwack

[thwak] /θwæk/
verb (used with object)
1.
to strike or beat vigorously with something flat; whack.
noun
2.
a sharp blow with something flat.
Origin
1520-30; imitative
Related forms
thwacker, noun
outthwack, verb (used with object)
unthwacked, adjective
British Dictionary definitions for thwack

thwack

/θwæk/
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
Derived Forms
thwacker, noun
Word Origin
C16: of imitative origin
Word Origin and History for thwack
v.

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