English▸ noun an abnormal growth formed in response to the presence of insect larvae, mites, or fungi on plants and trees, especially oaks:
a single grub feeds on its gall for two years before emerging
the witch hazel had developed leaf galls.
▪ [as modifier] denoting insects or mites that produce galls:
gall flies.
– ORIGIN Middle English: via Old French from Latin galla.