REIN, a guiding or controlling leather strap or thong, attached to the bit of a ridden or driven horse (see SADDLERY). The word is taken from the O. Fr. rene, modern rene, and is usually traced to a supposed Late Latin substantive retina formed from retinere, to hold back, restrain, cf. classical Latin retinaculum, halter. The word, usually in the plural, has been often used figuratively, as a type of that which guides, restrains or controls, e.g. in such phrases as the " reins of government," etc. The " reins," i.e. the kidneys (Lat. renes, cf. Gr. <t>pi]v, the midriff), or the place where the kidneys are situated, hence the loins, also, figuratively, the seat of the emotions or affections, must be distinguished.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)