| Firth (n.) An arm of the sea; a frith. Thesaurus Entries arm, armlet, bay, bayou, belt, bight, boca, cove, creek, estuary, euripus, fjord, frith, gulf, gut, harbor, inlet, kyle, loch, mouth, narrow, narrow seas, narrows, natural harbor, reach, road, roads, roadstead, sound, strait, straits | ![]() |