The Collaborative International Dictionary of English v.0.48:

Rye \Rye\ (r[imac]), n. [OE. rie, reie, AS. ryge; akin to Icel.
   rugr, Sw. r[*a]g, Dan. rug, D. rogge, OHG. rocco, roggo, G.
   rocken, roggen, Lith. rugei, Russ. roje, and perh. to Gr.
   'o`ryza rice. Cf. Rice.]
   1. (Bot.) A grain yielded by a hardy cereal grass (Secale
      cereale), closely allied to wheat; also, the plant
      itself. Rye constitutes a large portion of the breadstuff
      used by man.
      [1913 Webster]

   2. A disease in a hawk. --Ainsworth.
      [1913 Webster]

   Rye grass, Italian rye grass, (Bot.) See under Grass.
      See also Ray grass, and Darnel.

   Wild rye (Bot.), any plant of the genus Elymus, tall
      grasses with much the appearance of rye.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Secale cereale
    n 1: hardy annual cereal grass widely cultivated in northern
         Europe where its grain is the chief ingredient of black
         bread and in North America for forage and soil improvement
         [syn: rye, Secale cereale]