Early 19th century; earliest use found in The Universal Magazine. From French riverain (noun) person who lives on the banks of a river or near a river, or who owns land or property there, animal or plant whose habitat is on the banks of or in the vicinity of a river, (adjective) (of a place, estate, building, etc.) extending along a forest or (now chiefly) a way of communication such as a road, railway line, etc., situated on the banks of a river or other expanse of water (1848 or earlier; earlier in sense ‘(of a person) holding feudal possessions on the banks of or in the vicinity of a river’) from rivière + -ain. The sense of the English word was influenced by association with river early on, especially in the case of sense B. 2, which is unparalleled in French.