·vt To fill to overflow.
II. Thwack ·noun A heavy blow with something flat or heavy; a thump.
III. Thwack ·vt To strike with something flat or heavy; to bang, or thrash: to thump.
A great blow with a stick across the shoulders. ...
Dictionary of The Vulgar Tongue by Francis Grose
a hard blow. North. ...
A glossary of provincial and local words used in England by Francis Grose