Source : WordNet®

sour orange
     n 1: any of various common orange trees yielding sour or bitter
          fruit; used as grafting stock [syn: {Seville orange}, {bitter
          orange}, {bitter orange tree}, {bigarade}, {marmalade
          orange}, {Citrus aurantium}]
     2: highly acidic orange used especially in marmalade [syn: {bitter
        orange}, {Seville orange}]