Source : Webster's Revised Unabridged Dictionary (1913)

Rhythmer \Rhyth"mer\ (r[i^]th"m[~e]r or r[i^][th]"-), n.
   One who writes in rhythm, esp. in poetic rhythm or meter.
   [R.]

         One now scarce counted a rhythmer, formerly admitted
         for a poet.                              --Fuller.