Source : Webster's Revised Unabridged Dictionary (1913)

Amaranth \Am"a*ranth\, n. [L. amarantus, Gr. ?, unfading,
   amaranth; 'a priv. + ? to quench, cause to wither, fr. a root
   meaning to die, akin to E. mortal; -- so called because its
   flowers do not soon wither: cf. F. amarante. The spelling
   with th seems to be due to confusion with Gr. ? flower.]
   1. An imaginary flower supposed never to fade. [Poetic]

   2. (Bot.) A genus of ornamental annual plants ({Amaranthus})
      of many species, with green, purplish, or crimson flowers.

   2. A color inclining to purple.

Source : WordNet®

amaranth
     n 1: seed of amaranth plants used as a native cereal in Central
          and South America
     2: any of various plants of the genus Amaranthus having dense
        plumes of green or red flowers; often cultivated for food