maar vs crater

maar and crater both are nouns.

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

As nouns, crater is a hypernym of maar; that is, 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
crater: a bowl-shaped geological formation at the top of a volcano

Other hypernyms of maar include volcanic crater.

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