The Collaborative International Dictionary of English v.0.48:

Synonymic \Syn`o*nym"ic\ (s[i^]n`[o^]*n[i^]m"[i^]k), n. [Cf. G.
   synonymik. See Synonymous.] (Gram.)
   The science, or the scientific treatment, of synonymous
   words.
   [1913 Webster] Synonymic

The Collaborative International Dictionary of English v.0.48:

Synonymic \Syn`o*nym"ic\, Synonymical \Syn`o*nym"ic*al\, a.
   Of or pertaining to synonyms, or synonymic; synonymous.
   [1913 Webster]