rival

Rival is borrowed from Latin rivalis. As an adjective made from the noun rivus, “stream,” rivalis meant “of a brook or stream.” As a noun, rivalis was used to refer to those who use the same stream for water. Just as neighbors might dispute each other's rights to a common source of water, disagreement often arises when two people want something that only one can possess. Thus Latin rivalis also developed a sense relating to competition in other areas, and this sense came into English.