The Collaborative International Dictionary of English v.0.48:

Solidarity \Sol`i*dar"i*ty\, n. [F. solidarit['e], fr. solide.
   See Solid.]
   An entire union or consolidation of interests and
   responsibilities; fellowship; community.
   [1913 Webster]

         Solidarity [a word which we owe to the French
         Communists], signifies a fellowship in gain and loss,
         in honor and dishonor, in victory and defeat, a being,
         so to speak, all in the same boat.       --Trench.
   [1913 Webster]

         The solidarity . . . of Breton and Welsh poetry. --M.
                                                  Arnold.
   [1913 Webster]

WordNet (r) 3.0 (2006):

solidarity
    n 1: a union of interests or purposes or sympathies among
         members of a group