"bile," Old English galla (Anglian), gealla (W. Saxon) "gall, bile," from Proto-Germanic *gallon- (cf. Old Norse gall, Old Saxon, Old High German galla, German Galle), from PIE root *ghel- "gold, yellow, yellowish-green" (see Chloe). Informal sense of "impudence, boldness" first recorded American English 1882; but meaning "embittered spirit, rancor" is from c.1200, from the medieval theory of humors. Gall bladder recorded from 1670s.
"sore spot on a horse," Old English gealla "painful swelling," from Latin galla "gall, lump on plant," originally "oak apple," of uncertain origin. Perhaps from or influenced by gall (1) on notion of "poison-sore." German galle, Dutch gal also are from Latin.
"to make sore by chafing," mid-15c., from gall (n.2). Earlier "to have sores, be sore" (early 14c.). Figurative sense of "harass, irritate" is from 1570s. Related: Galled; galling.
An abnormal swelling of plant tissue, caused by injury or by parasitic organisms such as insects, mites, nematodes, and bacteria. Parasites stimulate the production of galls by secreting chemical irritants on or in the plant tissue. Galls stimulated by egg-laying parasites typically provide a protective environment in which the eggs can hatch and the pupae develop, and they usually do only minor damage to the host plant. Gall-stimulating fungi and microorganisms, such as the bacterium that causes crown gall, are generally considered to be plant diseases.