The Collaborative International Dictionary of English v.0.48:

Orris \Or"ris\, n. [Prob. corrupted from It. ireos iris. See
   Iris.] (Bot.)
   A plant of the genus Iris (Iris Florentina); a kind of
   flower-de-luce. Its rootstock has an odor resembling that of
   violets.
   [1913 Webster]

   Orris pea (Med.), an issue pea made from orris root.

   Orris root, the fragrant rootstock of the orris.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Iris florentina
    n 1: German iris having large white flowers with lavender-tinged
         falls and a fragrant rhizome [syn: Florentine iris,
         orris, Iris germanica florentina, Iris florentina]