Meaning

noun the sound made by a sharp swift blow

noun the act of hitting vigorously

verb hit hard

originUncertain. Originally Scottish; probably onomatopoeic, but compare Middle English thakken, from Old English þaccian (whence Modern thwack by conflation with whack). Sense 6 of the verb is likely a semantic loan from Malay hentam (“to strike; to do something carelessly”).

Etymology from Wiktionary, CC BY-SA 3.0