Source : Webster's Revised Unabridged Dictionary (1913)

Synonymy \Syn*on"y*my\, n. [L. synonymia, Gr. ? a synonym: cf.
   F. synonymie.]
   1. The quality of being synonymous; sameness of meaning.

   2. A system of synonyms.

   3. (Rhet.) A figure by which synonymous words are used to
      amplify a discourse.

Source : WordNet®

synonymy
     n : the semantic relation that holds between two words that can
         (in a given context) express the same meaning [syn: {synonymity},
          {synonymousness}]