The Collaborative International Dictionary of English v.0.48:

Sympathize \Sym"pa*thize\, v. i. [imp. & p. p. Sympathized; p.
   pr. & vb. n. Sympathizing.] [F. sympathiser. See
   Sympathy.]
   1. To have a common feeling, as of bodily pleasure or pain.
      [1913 Webster]

            The mind will sympathize so much with the anguish
            and debility of the body, that it will be too
            distracted to fix itself in meditation.
                                                  --Buckminster.
      [1913 Webster]

   2. To feel in consequence of what another feels; to be
      affected by feelings similar to those of another, in
      consequence of knowing the person to be thus affected.
      [1913 Webster]

            Their countrymen . . . sympathized with their heroes
            in all their adventures.              --Addison.
      [1913 Webster]

   3. To agree; to be in accord; to harmonize. --Dryden.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sympathize \Sym"pa*thize\, v. t.
   1. To experience together. [Obs.] "This sympathized . . .
      error." --Shak.
      [1913 Webster]

   2. To ansew to; to correspond to. [Obs.] --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sympathize
    v 1: share the feelings of; understand the sentiments of [syn:
         sympathize, sympathise]
    2: be understanding of; "You don't need to explain--I
       understand!" [syn: sympathize, sympathise, empathize,
       empathise, understand]
    3: to feel or express sympathy or compassion [syn:
       commiserate, sympathize, sympathise]