NOUN (2)

1. a specialist in philosophy;

2. a wise person who is calm and rational; someone who lives a life of reason with equanimity;

The Collaborative International Dictionary of English v.0.48:

Philosopher \Phi*los"o*pher\, n. [OE. philosophre, F.
   philosophe, L. philosophus, Gr. filo`sofos; fi`los loving +
   sofo`s wise. Cf. Philosophy.]
   1. One who philosophizes; one versed in, or devoted to,
      philosophy.
      [1913 Webster]

            Then certain philosophers of the Epicureans, and of
            the Stoics, encountered him.          --Acts xvii.
                                                  18.
      [1913 Webster]

   2. One who reduces the principles of philosophy to practice
      in the conduct of life; one who lives according to the
      rules of practical wisdom; one who meets or regards all
      vicissitudes with calmness.
      [1913 Webster]

   3. An alchemist. [Obs.] --Chaucer.
      [1913 Webster]

   Philosopher's stone, an imaginary stone which the
      alchemists formerly sought as the instrument of converting
      the baser metals into gold.
      [1913 Webster] Philosophic

WordNet (r) 3.0 (2006):

philosopher
    n 1: a specialist in philosophy
    2: a wise person who is calm and rational; someone who lives a
       life of reason with equanimity