fem. proper name (c. 1300), from Old French Margaret (French Marguerite), from Late Latin Margarita, female name, literally "pearl," from Greek margaritēs (lithos) "pearl," of unknown origin.
OED writes, "probably adopted from some Oriental language" [OED]. Beekes writes, "An oriental loanword, mostly assumed to be from Iranian" and cites Middle Persian marvarit "pearl." He adds, "The older view" derives it from Sanskrit manjari "pearl; flowering bead," "but the late and rare occurrence of both the Skt. and Greek form is no support for a direct identification." He also reports a suggested origin in Iranian *mrga-ahri-ita- "born from the shell of a bird" = "oyster."
Arabic marjan probably is from Greek, via Syraic marganitha. The word was widely perverted in Germanic languages by folk-etymology, for example Old English meregrot, which has been altered as if it meant literally "sea-pebble." The word was used figuratively in Middle English for "that which is precious or excellent, a priceless quality or attribute." Derk margaryte was "a corrupted conscience."