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|n.||1.||(Zool.) Any one of three species of South American ostriches of the genera Rhea and Pterocnemia, especially the smallest, Pterocnemia pennata (formerly Rhea Americana), called also the common rhea. They are tall fast-running flightless birds similar to ostriches but three-toed, found from Peru to the Straits of Magellan. See Rhea.|