interneuron (n.)

"a nerve cell with its appendages," 1891, from German Neuron, from Greek neuron (see neuro-). Used earlier (1884) for "the spinal cord and brain, considered as one."

word-forming element used freely in English, "between, among, during," from Latin inter (prep., adv.) "among, between, betwixt, in the midst of" (also used extensively as a prefix), from PIE *enter "between, among" (source also of Sanskrit antar, Old Persian antar "among, between," Greek entera (plural) "intestines," Old Irish eter, Old Welsh ithr "among, between," Gothic undar, Old English under "under"), a comparative of root *en "in."

A living prefix in English from 15c. and used with Germanic as well as Latinate words. Spelled entre- in French; most words borrowed into English in that form were re-spelled 16c. to conform with Latin except entertain, enterprise. In Latin, spelling shifted to intel- before -l-, hence intelligence, etc.

Proto-Indo-European root meaning "to shout." It forms all or part of: announce; denounce; enunciate; nuncio; pronounce; renounce.

It is the hypothetical source of/evidence for its existence is provided by: Greek neuo "to nod, beckon," Latin nuntius "messenger," Old Irish noid "make known."