ganglionn.[L. ganglion a sort of swelling or excrescence, a tumor under the skin, Gr. : cf. F. ganglion.]1. (Anat.) A mass or knot of nervous matter, including nerve cells, usually forming an enlargement in the course of a nerve.()2. (Med.) A globular, hard, indolent tumor, situated somewhere on a tendon, and commonly formed by the effusion of a viscid fluid into it; -- called also weeping sinew.()Ganglion cell, a nerve cell. See Illust. under Bipolar.()