late 14c., via Old French (13c.) or Latin, from Greek Amazon (mostly in plural Amazones) "one of a race of female warriors in Scythia," probably from an unknown non-Indo-European word, or possibly from an Iranian compound *ha-maz-an- "(one) fighting together" [Watkins], but in folk etymology long derived from a- "without" + mazos, variant of mastos "breast;" hence the story that the Amazons cut or burned off one breast so they could draw bowstrings more efficiently. Also used generally in early Modern English of female warriors; strong, tall, or masculine women; and the queen in chess.
The river in South America (originally called by the Spanish Rio Santa Maria de la Mar Dulce) rechristened by Francisco de Orellana, 1541, after an encounter with female warriors of the Tapuyas (or, as some say, beardless, long-haired male tribesmen). Others hold that the river name is a corruption of a native word in Tupi or Guarani meaning "wave").