Thwack (thwăk), v. t. [imp. & p. p.Thwacked (?); p. pr. & vb. n.Thwacking.] [Cf. OE. thakken to stroke, AS. þaccian, E. whack.] 1. To strike with something flat or heavy; to bang, or thrash: to thump. “A distant thwacking sound.” W. Irving.
2. To fill to overflow. Stanyhurst.