define bonk
verb (used with or without object), Slang. 1. to hit, strike, collide, etc.: to get bonked on the head; cars bonking into each other. Origin of bonk. perhaps variant of bong1.
Etymology, usage, and synonyms. The term bonk for fatigue is presumably derived from the original meaning to hit, and dates back at least half a century. Its earliest citation in the Oxford English Dictionary is a 1952 article in the Daily Mail.