Gan"gli*on (?), n.; pl. L. Ganglia (#), E. Ganglions (#). [L. ganglion a sort of swelling or excrescence, a tumor under the skin, Gr. &?;: cf. F. ganglion.] 1. (Anat.) (a) A mass or knot of nervous matter, including nerve cells, usually forming an enlargement in the course of a nerve. (b) A node, or gland in the lymphatic system; as, a lymphatic ganglion.

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.

• (anatomy) a mass of tissue, outside of the brain, containing a cluster of interconnecting nerve cells
  
• By extension, a centre of power or authority