Ganglion, from the Greek gagglion, tumor or swelling. Hippocrates, in the 5th century B.C., used the term for any growth that could be felt beneath the skin. This use continues today, but only for the "ganglion cysts" of tendons or joint capsules most frequently seen at the wrist.
A ganglion cyst
The Roman physician Galen, in the 2nd century, used the term initially for abnormal swellings associated with nerves but ultimately for normal "swellings" of nervous system structures as well, the sympathetic ganglia in particular.
1700 years later, in the 19th century, it was determined that the sympathetic ganglia were composed of large collections of neuron cell bodies, and the definition of ganglia soon expanded to include all such structures outside the brain and spinal cord, including the prevertebral sympathetic ganglia, numerous parasympathetic ganglia, and the dorsal root ganglia of the spinal nerves.
Collections of neuron cell bodies within the central nervous are usually called nuclei and not ganglia, though the use of the term persists in the basal ganglia of the cerebrum.
Other than for the ganglion cysts, the term is no longer used for abnormalities.