The Collaborative International Dictionary of English v.0.48:

Reunion \Re*un"ion\, n. [Pref. re- + union: cf. F. r['e]union.]
   1. A second union; union formed anew after separation,
      secession, or discord; as, a reunion of parts or particles
      of matter; a reunion of parties or sects.
      [1913 Webster]

   2. An assembling of persons who have been separated, as of a
      family, or the members of a disbanded regiment; an
      assembly so composed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reunion
    n 1: a party of former associates who have come together again
    2: the act of coming together again; "monetary unification
       precipitated the reunification of the German state in October
       1990" [syn: reunion, reunification]