merus

Traditionally derived from a Proto-Indo-European *mer- (“to sparkle, glimmer, gleam”), and compared with Ancient Greek μαρμαίρω (marmaírō, “to flash, sparkle”), Sanskrit मरीचि (marīci, “beam, ray”), Old Irish emer, and Proto-Germanic *mērijaz (“famous”). However, De Vaan expresses skepticism at the semantic shift from "shine" → "pure", and prefers Puhvel's derivation from Proto-Indo-European *merH-o-s, from a Proto-Indo-European *merH- (“to remain, be distilled and pure”), whence Hittite [script needed] (marri, “just so, gratuitously”). Old English āmerian (“to purify”) is a borrowing from the Latin, according to Kroonen.