Source : Webster's Revised Unabridged Dictionary (1913)

Citron \Cit"ron\ (s[i^]t"r[u^]n), n. [F. citron, LL. citro, fr.
   L. citrus citron tree (cf. citreum, sc. malum, a citron),
   from Gr. ki`tron citron]
   1. (Bot) A fruit resembling a lemon, but larger, and
      pleasantly aromatic. The thick rind, when candied, is the
      citron of commerce.

   2. A citron tree.

   3. A citron melon.

   {Citron melon}.
      (a) A small variety of muskmelon with sugary greenish
          flesh.
      (b) A small variety of watermelon, whose solid white flesh
          is used in making sweetmeats and preserves.

   {Citron tree} (Bot.), the tree which bears citrons. It was
      probably a native of northern India, and is now understood
      to be the typical form of {Citrus Medica}.

Source : WordNet®

citron tree
     n : thorny evergreen small tree or shrub of India widely
         cultivated for its large lemonlike fruits that have thick
         warty rind [syn: {citron}, {Citrus medica}]