maar vs volcanic crater

maar and volcanic crater both are nouns.

Word	Noun	Adjective	Verb	Adverb
maar	Yes	No	No	No
volcanic crater	Yes	No	No	No

As nouns, volcanic crater is a hypernym of maar; that is, volcanic crater is a word with a broader meaning than maar:

maar: a flat-bottomed volcanic crater that was formed by an explosion; often filled with water
volcanic crater: a bowl-shaped geological formation at the top of a volcano

Other hypernyms of maar include crater.

maar (noun)	volcanic crater (noun)
a flat-bottomed volcanic crater that was formed by an explosion; often filled with water	a bowl-shaped geological formation at the top of a volcano