crater vs caldera

crater and caldera both are nouns.

Word	Noun	Adjective	Verb	Adverb
crater	Yes	No	No	No
caldera	Yes	No	No	No

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

crater: a bowl-shaped geological formation at the top of a volcano
caldera: a large crater caused by the violent explosion of a volcano that collapses into a depression

Other hyponyms of crater include maar.

crater (noun)	caldera (noun)
a bowl-shaped depression formed by the impact of a meteorite or bomb	a large crater caused by the violent explosion of a volcano that collapses into a depression
a bowl-shaped geological formation at the top of a volcano