ganglion

Concise Oxford English Dictionary © 2008 Oxford University Press:
ganglion /ˈgaŋglɪən/

▶noun (pl. ganglia or ganglions)

• 1 Anatomy a structure containing a number of nerve cells, often forming a swelling on a nerve fibre.

  ■ a well-defined mass of grey matter within the central nervous system.

• 2 Medicine an abnormal benign swelling on a tendon sheath.

– derivatives
ganglionic adjective.

– origin C17: from Gk ganglion ‘tumour on or near sinews or tendons’.