concave shape vs trough

concave shape and trough both are nouns.

Word	Noun	Adjective	Verb	Adverb
concave shape	Yes	No	No	No
trough	Yes	No	No	No

As nouns, trough is a hyponym of concave shape; that is, trough is a word with a more specific, narrower meaning than concave shape:

concave shape (noun)	trough (noun)
a shape that curves or bends inward	a channel along the eaves or on the roof; collects and carries away rainwater
	a container (usually in a barn or stable) from which cattle or horses feed
	a long narrow shallow receptacle
	a narrow depression (as in the earth or between ocean waves or in the ocean bed)
	a treasury for government funds
	a concave shape with an open top