"pertaining to the seashore," 1650s, from Latin littoralis "of or belonging to the seashore," from litus (genitive litoris) "seashore, coast, seaside, beach, strand," from Proto-Italic *leitos, a word of unknown origin, possibly from PIE root *lei- "to flow" [Watkins], but de Vaan finds a better candidate in the PIE root *leit- (2) "to go forth" (see lead (v.1)), with sense evolution "the going away," hence "the edge."
The noun meaning "part of a country lying along the coast" is from 1828, from Italian littorale, originally an adjective, from Latin littoralis. Compare Lido.
