depression vs lowland

depression and lowland both are nouns.

Word	Noun	Adjective	Verb	Adverb
depression	Yes	No	No	No
lowland	Yes	Yes	No	No

As nouns, lowland is a hyponym of depression; that is, lowland is a word with a more specific, narrower meaning than depression:

Other hyponyms of depression include basin, bed, bottom, crater, hole, hollow, sink, sinkhole, swallow hole, deep, oceanic abyss, trench, trough, vale, valley.

depression (noun)	lowland (noun)
pushing down	low level country
sad feelings of gloom and inadequacy
a sunken or depressed geological formation
angular distance below the horizon (especially of a celestial object)
a concavity in a surface produced by pressing
a mental state characterized by a pessimistic sense of inadequacy and a despondent lack of activity
an air mass of lower pressure; often brings precipitation
a long-term economic state characterized by unemployment and low prices and low levels of trade and investment
a state of depression and anhedonia so severe as to require clinical intervention

depression (adjective)	lowland (adjective)
	of relatively low or level country