basin - a natural depression in the surface of the land often with a lake at the bottom of it; "the basin of the Great Salt Lake"

bed, bottom - a depression forming the ground under a body of water; "he searched for treasure on the ocean bed"

crater - a bowl-shaped depression formed by the impact of a meteorite or bomb

geological formation, formation - (geology) the geological features of the earth

hollow, hole - a depression hollowed out of solid matter

lowland - low level country

sinkhole, swallow hole, sink - a depression in the ground communicating with a subterranean passage (especially in limestone) and formed by solution or by collapse of a cavern roof

oceanic abyss, trench, deep - a long steep-sided depression in the ocean floor

trough - a narrow depression (as in the earth or between ocean waves or in the ocean bed)

vale, valley - a long depression in the surface of the land that usually contains a river