The Collaborative International Dictionary of English v.0.48:

Pleurisy \Pleu"ri*sy\, n. [F. pleur['e]sie, L. pleurisis,
   pleuritis, Gr pleyri^tis (sc. no`sos), fr. pleyra` rib,
   side.] (Med.)
   An inflammation of the pleura, usually accompanied with
   fever, pain, difficult respiration, and cough, and with
   exudation into the pleural cavity.
   [1913 Webster]

   Pleurisy root. (Bot.)
   (a) The large tuberous root of a kind of milkweed (Asclepias
       tuberosa) which is used as a remedy for pleuritic and
       other diseases.
   (b) The plant itself, which has deep orange-colored flowers;
       -- called also butterfly weed.
       [1913 Webster]

WordNet (r) 3.0 (2006):

pleurisy root
    n 1: erect perennial of eastern and southern United States
         having showy orange flowers [syn: butterfly weed, orange
         milkweed, chigger flower, chiggerflower, pleurisy
         root, tuber root, Indian paintbrush, Asclepias
         tuberosa]