bitter orange, Seville orange, sour orange - highly acidic orange used especially in marmalade

genus Citrus - orange; lemon; lime; etc.

orange tree, orange - any citrus tree bearing oranges

orange - round yellow to orange fruit of any of several citrus trees

bigarade, bitter orange, bitter orange tree, Citrus aurantium, marmalade orange, Seville orange, sour orange - any of various common orange trees yielding sour or bitter fruit; used as grafting stock