Rye /(rī)/ Rye n. A grain yielded by a hardy cereal grass (Secale cereale), closely allied to wheat; also, the plant itself. Rye constitutes a large portion of the breadstuff used by man. (Bot.) A disease in a hawk. Phrases & Compounds Rye grass See under Grass. See also Ray grass, and Darnel. Wild rye any plant of the genus Elymus, tall grasses with much the appearance of rye.