Source : Webster's Revised Unabridged Dictionary (1913)

Synchronism \Syn"chro*nism\, n. [Gr. ?, fr. ? to be contemporary
   with, from ? synchronous. See {Synchronous}.]
   1. The concurrence of events in time; simultaneousness.

   2. The tabular arrangement of historical events and
      personages, according to their dates.

   3. (Paint.) A representation, in the same picture, of two or
      events which occured at different times.

Source : WordNet®

synchronism
     n : the relation that exists when things occur at the same time;
         "the drug produces an increased synchrony of the brain
         waves" [syn: {synchrony}, {synchronicity}, {synchroneity},
          {synchronization}, {synchronisation}, {synchronizing}]
         [ant: {asynchronism}, {asynchronism}, {asynchronism}]