- The sound of a heavy smack.
2007 December 2, Stephanie Zacharek, “Mad”, in New York Times:
- THE COMPLETELY MAD DON MARTIN, a two-volume honker that includes every drawing Martin ever published in the magazine, answers the question with a definitive thwap: Martin's cartoons are still weird.
- To make, or cause to make, a heavy smacking sound.
2004, Anthony Doerr, About Grace, page 241:
- Reflectors in the road thwapped beneath the tires, setting a regular, almost reassuring pace.