crater vs maar

crater and maar both are nouns.

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

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

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

Other hyponyms of crater include caldera.

crater (noun)	maar (noun)
a bowl-shaped depression formed by the impact of a meteorite or bomb	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