bunchyoudaoicibaDictYouDict[bunch 词源字典]
bunch: [14] Bunch originally meant ‘swelling’ (the first text recorded as containing the word, the Middle English poem Body and Soul 1325, speaks of ragged folk ‘with broad bunches on their back’), but we have no real clues as to its source. Perhaps, like bump, it was ultimately imitative of the sound of hitting something, the sense ‘swelling’ being the result of the blows. The first hints of the modern sense ‘cluster, collection’ come in the mid-15th century in the phrase bunch of straw, although how this derived from ‘swelling’ is not clear.
[bunch etymology, bunch origin, 英语词源]
bunch (n.)youdaoicibaDictYouDict
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.
bunch (v.)youdaoicibaDictYouDict
"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.