1911 Encyclopædia Britannica/Rival

RIVAL, one who competes with another, one who strives to out-do or excel another or to gain an object or end before or in preference to another. The Latin rivalis, which was in classical Latin used of a competitor in love, meant by derivation one who used the same brook or stream (rivus) as another, hence a neighbour; thus in the Digest, xliii. 20, i. 26, “si inter rivales, id est qui per eundem rivum aquam ducunt, sit contentio de aquae usu.” The term naturally applied more particularly to those who lived on opposite sides of a stream which would be a frequent subject of dispute as to rights.