n. (Med.) An inflammation of the pleura, usually accompanied with fever, pain, difficult respiration, and cough, and with exudation into the pleural cavity. 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.