sour orange

  1. an orange tree (Citrus aurantium) widely grown as a rootstock for grafting other citrus trees
  2. its fruit, used in making marmalade

See sour orange in American Heritage Dictionary 4

noun In both senses also called bigarade, bitter orange, Seville orange.
  1. A spiny evergreen tree (Citrus aurantium) native to southern Vietnam and widely cultivated in warmer regions, having globose, reddish-orange, highly acidic fruit.
  2. The fruit of this tree.
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