Meaning

noun a flat-bottomed volcanic crater that was formed by an explosion; often filled with water

originBorrowed from German Maar; English usage from 1825, from Vulgar Latin *mara (“standing water”), from Latin mare (“sea”). Doublet of mare (“a large, dark plain; a lake on Titan”) and mere (“a body of standing water”).

Etymology from Wiktionary, CC BY-SA 3.0