late 14c., from Old French pleurisie (13c., Modern French pleurésie) and directly from Late Latin pleurisis "pleurisy," alteration of Latin pleuritis "pain in the side," from Greek pleuritis, from pleura "side of the body, rib," of unknown origin. Spelling altered in Late Latin on model of Latin stem plur- "more" (as in Medieval Latin pluritas "multitude"), as if in reference to "excess of humors."