The Collaborative International Dictionary of English v.0.48:

Syncopation \Syn`co*pa"tion\, n.
   1. (Gram.) The act of syncopating; the contraction of a word
      by taking one or more letters or syllables from the
      middle; syncope.
      [1913 Webster]

   2. (Mus.) The act of syncopating; a peculiar figure of
      rhythm, or rhythmical alteration, which consists in
      welding into one tone the second half of one beat with the
      first half of the beat which follows.
      [1913 Webster]

WordNet (r) 3.0 (2006):

syncopation
    n 1: (phonology) the loss of sounds from within a word (as in
         `fo'c'sle' for `forecastle') [syn: syncope,
         syncopation]
    2: a musical rhythm accenting a normally weak beat
    3: music (especially dance music) that has a syncopated rhythm