THESAURUS
Firth
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
ROGET THESAURUS
Firth
Lake
N
gulf, lake, land covered with water, gulf, gulph, bay, inlet, bight, estuary, arm of the sea, bayou, fiord, armlet, frith, firth, ostiary, mouth, lagune, lagoon, indraught, cove, creek, natural harbor, roads, strait, narrows, Euripus, sound, belt, gut, kyles, continental slope, continental shelf, lake, loch, lough, mere, tarn, plash, broad, pond, pool, lin, puddle, slab, well, artesian well, standing water, dead water, sheet of water, fish pond, mill pond, ditch, dike, dyke, dam, reservoir, alberca, barachois, hog wallow, lacustrine.