littoral (adj.) Look up littoral at
"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.