The Collaborative International Dictionary of English v.0.48:

Mandarin \Man`da*rin"\, n. [Pg. mandarim, from Malay mantr[imac]
   minister of state, prop. a Hind. word, fr. Skr. mantrin a
   counselor, manira a counsel, man to think.]
   1. A Chinese public officer or nobleman; a civil or military
      official in China and Annam.
      [1913 Webster]

   2. Hence: A powerful government official or bureaucrat,
      especially one who is pedantic and has a strong sense of
      his own importance and privelege.
      [PJC]

   3. Hence: A member of an influential, powerful or elite
      group, espcially within artistic or intellectual circles;
      -- used especially of elder members who are traditionalist
      or conservative about their specialties.
      [PJC]

   5. The form of the Chinese language spoken by members of the
      Chinese Imperial Court an officials of the empire.
      [PJC]

   6. Any of several closely related dialects of the Chinese
      language spoken by a mojority of the population of China,
      the standard variety of which is spoken in the region
      around Beijing.
      [PJC]

   7. (Bot.) A small flattish reddish-orange loose-skinned
      orange, with an easily separable rind. It is thought to be
      of Chinese origin, and is counted a distinct species
      (Citrus reticulata formerly Citrus nobilis); called
      also mandarin orange and tangerine.
      [1913 Webster]

   Mandarin language, the spoken or colloquial language of
      educated people in China.

   Mandarin yellow (Chem.), an artificial aniline dyestuff
      used for coloring silk and wool, and regarded as a complex
      derivative of quinoline.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

mandarin orange \man`da*rin" or"ange\, n.
   1. A shrub or small tree (Citrus reticulata) 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 Southeast Asia.

   Syn: mandarin orange tree.
        [WordNet 1.5]

   2. Same as mandarin[7].
      [1913 Webster]

WordNet (r) 3.0 (2006):

Citrus reticulata
    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,
         mandarin orange tree, Citrus reticulata]