Entry 3 senses · 2 variants Webster, 1913 Pleura · Pleu·ra · IPA /ˈplʊɹ.ə/ n. n. 01 n. pl. of Pleuron. 1. pl. of Pleuron. See: Pleuron 02 n. The smooth serous membrane which closely covers the lungs and the adjacent surfaces of the thorax; the pleural membrane. pl. Pleuræ, Pleuras ((#)) 1. The smooth serous membrane which closely covers the lungs and the adjacent surfaces of the thorax; the pleural membrane.(Anat.) 2. Same as Pleuron.(Zool.) See: Pleuron