The Collaborative International Dictionary of English v.0.48:

Fraternize \Fra"ter*nize\ (? or ?; 277), v. i. [imp. & p. p.
   Fraternized; p. pr. & vb. n.. Fraternizing.] [Cf. F.
   fraterniser.]
   To associate or hold fellowship as brothers, or as men of
   like occupation or character; to have brotherly feelings.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fraternize \Fra"ter*nize\, v. t.
   To bring into fellowship or brotherly sympathy.
   [1913 Webster]

         Correspondence for fraternizing the two nations.
                                                  --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fraternize
    v 1: be on friendly terms with someone, as if with a brother,
         especially with an enemy [syn: fraternize, fraternise]