Meaning

noun a hard blow with a flat object

verb deliver a hard blow to

originThe verb is probably: * partly onomatopoeic, from the sound of something being beaten (compare whack); and * partly derived from Late Middle English twakken, twake (“to hit (someone) with something; to pat; to stroke”), probably from Middle English thakken, thakke (“to dab; to pat; to stroke”) [and other forms] (whence thack (obsolete except Britain, dialectal)), from Old English þaccian (“to…

Etymology from Wiktionary, CC BY-SA 3.0