early 14c., "protuberance on the body, swelling," perhaps echoic of the sound of hitting and connected to bump (compare, possibly in similar relationship, hump/hunch).The sense of "cluster" is mid-15c.; connection with the earlier sense is obscure, and this may be a separate word, perhaps through a nasalized form of Old French bouge (2), 15c., from Flemish boudje diminutive of boud "bundle." Meaning "a lot, a group" is from 1620s.

"to bulge out," late 14c., from bunch, n.. Meaning "to gather up in a bunch" (transitive) is from 1828; sense of "to crowd together" (intransitive) is from 1873. Related: Bunched; bunching.