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Any of several tall, clump-forming prairie grasses of the genus Tripsacum native chiefly to Central and North America; especially (more fully "eastern gamagrass") Tripsacum dactyloides, cultivated in the southern United States and elsewhere as a forage grass.
Mid 19th century. Probably from a variant or alteration of Spanish grama or its etymon grama + grass, although grama normally denotes a different type of grass.