back O.E. bæc "back, backwards, behind," from P.Gmc. *bakam (cf. O.S., M.Du. bak, O.Fris. bek), with no known connections outside Germanic. The cognates mostly have been ousted in this sense in other modern Gmc. languages by words akin to Modern English ridge (cf. Dan. ryg, Ger. Rücken). Many I.E. languages show signs of once having distinguished the horizontal back of an animal (or a mountain range) from the upright back of a human. In other cases, a modern word for "back" may come from a word related to "spine" (It. schiena, Rus. spina) or "shoulder, shoulder blade" (Sp. espalda, Pol.