Source : Webster's Revised Unabridged Dictionary (1913)

Rhymeless \Rhyme"less\, a.
   Destitute of rhyme. --Bp. Hall.

Source : WordNet®

rhymeless
     adj : not having rhyme; "writing unrhymed blank verse is like
           playing tennis without a net" [syn: {unrhymed}, {unrimed},
            {rimeless}] [ant: {rhymed}]