NOUN (2)

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;

The Collaborative International Dictionary of English v.0.48:

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]
      [1913 Webster]

   2. (Bot.) A genus of ornamental annual plants (Amaranthus)
      of many species, with green, purplish, or crimson flowers.
      [1913 Webster]

   3. A color inclining to purple.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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