ganglion

The word 'ganglion' entered English in the late 17th century via Latin from the Greek 'γάγγλιον' (gánglion), meaning a "knot" or "swelling under the skin." The Greek term itself is of unknown, possibly pre-Greek origin. In ancient medical contexts, it was used to describe any subcutaneous, tumor-like knot. This literal sense of a "swelling" or "knot" was directly adopted into early anatomical terminology to describe the distinctive, knot-like clusters of nerve cell bodies found outside the central nervous system. The modern, abstract medical meaning thus evolved directly from this concrete, physical description of the structure's appearance.

The word is a simplex loanword from Greek. It cannot be meaningfully segmented into smaller, independent morphemes using its modern English spelling without resorting to reconstructed Greek forms (e.g., gangli-).