Definition
A gall (syn. tumor) is an abnormal swelling or localized outgrowth, often roughly spherical, produced by a plant as a result of attack by a fungus, bacterium, nematode, insect, or other organism.
Etymology. "sore spot on a horse," O.E. gealla "painful swelling," from L. galla "gall, lump on plant," originally "oak apple," of uncertain origin. Perhaps from or influenced by notion of "poison-sore." The verb meaning "to make sore by chafing" is from c.1440; fig. sense of "harass, irritate" is from 1573.