Source : Webster's Revised Unabridged Dictionary (1913)

Orange \Or"ange\, n. [F.; cf. It. arancia, arancio, LL. arangia,
   Sp. naranjia, Pg. laranja; all fr. Ar. n[=a]ranj, Per.
   n[=a]ranj, n[=a]rang; cf. Skr. n[=a]ranga orange tree. The o-
   in F. orange is due to confusion with or gold, L. aurum,
   because the orange resembles gold in color.]
   1. The fruit of a tree of the genus {Citrus} ({C.
      Aurantium}). It is usually round, and consists of pulpy
      carpels, commonly ten in number, inclosed in a leathery
      rind, which is easily separable, and is reddish yellow
      when ripe.

   Note: There are numerous varieties of oranges; as, the
         {bitter orange}, which is supposed to be the original
         stock; the {navel orange}, which has the rudiment of a
         second orange imbedded in the top of the fruit; the
         {blood orange}, with a reddish juice; and the {horned
         orange}, in which the carpels are partly separated.

   2. (Bot.) The tree that bears oranges; the orange tree.

   3. The color of an orange; reddish yellow.

   {Mandarin orange}. See {Mandarin}.

   {Mock orange} (Bot.), any species of shrubs of the genus
      {Philadelphus}, which have whitish and often fragrant
      blossoms.

   {Native orange}, or {Orange thorn} (Bot.), an Australian
      shrub ({Citriobatus parviflorus}); also, its edible yellow
      berries.

   {Orange bird} (Zo["o]l.), a tanager of Jamaica ({Tanagra
      zena}); -- so called from its bright orange breast.

   {Orange cowry} (Zo["o]l.), a large, handsome cowry
      ({Cypr[ae]a aurantia}), highly valued by collectors of
      shells on account of its rarity.

   {Orange grass} (Bot.), an inconspicuous annual American plant
      ({Hypericum Sarothra}), having minute, deep yellow
      flowers.

   {Orange oil} (Chem.), an oily, terpenelike substance obtained
      from orange rind, and distinct from neroli oil, which is
      obtained from the flowers.

   {Orange pekoe}, a kind of black tea.

   {Orange pippin}, an orange-colored apple with acid flavor.

   {Quito orange}, the orangelike fruit of a shrubby species of
      nightshade ({Solanum Quitoense}), native in Quito.

   {Orange scale} (Zo["o]l.) any species of scale insects which
      infests orange trees; especially, the purple scale
      ({Mytilaspis citricola}), the long scale ({M. Gloveri}),
      and the red scale ({Aspidiotus Aurantii}).

Source : WordNet®

mandarin orange
     n 1: shrub or small tree having flattened globose fruit with very
          sweet aromatic pulp and thin yellow-orange to
          flame-orange rind that is loose and easily removed;
          native to southeastern Asia [syn: {mandarin}, {mandarin
          orange tree}, {Citrus reticulata}]
     2: a somewhat flat reddish-orange loose-skinned citrus of China
        [syn: {mandarin}]