The Collaborative International Dictionary of English v.0.48:

Purpura \Pur"pu*ra\, n. [L., purple, purple fish: cf. F.
   purpura. See Purple.]
   1. (Med.) A disease characterized by livid spots on the skin
      from extravasated blood, with loss of muscular strength,
      pain in the limbs, and mental dejection; the purples.
      --Dunglison.
      [1913 Webster]

   2. (Zool.) A genus of marine gastropods, usually having a
      rough and thick shell. Some species yield a purple dye.
      [1913 Webster]

WordNet (r) 3.0 (2006):

purpura
    n 1: any of several blood diseases causing subcutaneous bleeding
         [syn: purpura, peliosis]