The Collaborative International Dictionary of English v.0.48:

Pleura \Pleu"ra\, n.,
   pl. of Pleuron.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pleura \Pleu"ra\, n.; pl. L. Pleur[ae], E. Pleuras. [NL., n.
   fem., fr. Gr. ? a rib, the side.]
   1. (Anat.)
      (a) The smooth serous membrane which closely covers the
          lungs and the adjacent surfaces of the thorax; the
          pleural membrane.
      (b) The closed sac formed by the pleural membrane about
          each lung, or the fold of membrane connecting each
          lung with the body wall.
          [1913 Webster]

   2. (Zool.) Same as Pleuron.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pleuron \Pleu"ron\, n.; pl. Pleura. [NL., fr. Gr. ? a rib.]
   (Zool.)
   (a) One of the sides of an animal.
   (b) One of the lateral pieces of a somite of an insect.
   (c) One of lateral processes of a somite of a crustacean.
       [1913 Webster]

WordNet (r) 3.0 (2006):

pleura
    n 1: the thin serous membrane around the lungs and inner walls
         of the chest