The Collaborative International Dictionary of English v.0.48:
Gall \Gall\ (g[add]l), n. [F. galle, noix de galle, fr. L.
An excrescence of any form produced on any part of a plant by
insects or their larvae. They are most commonly caused by
small Hymenoptera and Diptera which puncture the bark and lay
their eggs in the wounds. The larvae live within the galls.
Some galls are due to aphids, mites, etc. See Gallnut.
Note: The galls, or gallnuts, of commerce are produced by
insects of the genus Cynips, chiefly on an oak
(Quercus infectoria syn. Quercus Lusitanica) of
Western Asia and Southern Europe. They contain much
tannin, and are used in the manufacture of that article
and for making ink and a black dye, as well as in
Gall insect (Zool.), any insect that produces galls.
Gall midge (Zool.), any small dipterous insect that
Gall oak, the oak (Quercus infectoria) which yields the
galls of commerce.
Gall of glass, the neutral salt skimmed off from the
surface of melted crown glass;- called also glass gall
and sandiver. --Ure.
Gall wasp. (Zool.) See Gallfly.