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