Definitions

1. verb

to hit or strike something with a sudden, loud impact

“She let out a loud cry when she accidentally thwacked her finger with the hammer.”

2. noun

a loud, sharp sound of something hitting or striking something else

“The thwack of the baseball bat against the ball was music to his ears.”

3. interjection

expressing shock, surprise, or pain

“Ouch! That was a thwack to the back, you big galoot!”