definition of citrus
citrus. pl. citrus or citÂ·rusÂ·es. noun. 1  Any of various evergreen, usually spiny shrubs or trees of the genus Citrus and other genera in the family Rutaceae, such as the grapefruit, lemon, and orange, native to South and Southeast Asia and widely cultivated for their juicy edible fruits with a leathery aromatic rind. 2  The fruit of any of these plants.