the.com/bump

means A light collision or jolt — a knock, swelling, or small forceful contact, as when two things (or fists) meet briefly.

from Likely imitative in origin — a word built from its own sound, like 'thump' or 'bang,' mimicking the dull noise of one solid thing striking another. It surfaces in English in the 1500s meaning a sudden blow, and only later picked up its sense of a swelling raised by such a blow, then a bulge in a road, then — much more recently — the friendly knock of knuckles that gave us the fist bump.