medulla n.

hindmost segment of the brain, 1670s, from Latin medulla, literally "marrow," also "pith of plants," a word of uncertain origin, but probably from PIE *smer-u- "marrow" (source also of Old Irish smiur, Welsh mer "marrow"), perhaps influenced by medius "middle." The word was used in the Latin senses in Middle English. Related: Medullar; medullary.