ganglion

1. (neuroanatomy)Examples: "[T]he wonderfully diversified instincts, mental powers, and affections of ants are generally known, yet their cerebral ganglia are not so large as the quarter of a small pin's head."

2. (neuroanatomy)Examples: "The yawning gap in neuroscientists’ understanding of their topic is in the intermediate scale of the brain’s anatomy. Science has a passable knowledge of how individual nerve cells, known as neurons, work. It also knows which visible lobes and ganglia of the brain do what. But how the neurons are organised in these lobes and ganglia remains obscure."Synonyms: nucleus

3. (transferred sense) A centre of intellectual or industrial force, activity, etc.

4. (pathology) A benign cystic tumour on a tendon sheath or joint capsule.Synonyms: ganglion cyst