Source : Webster's Revised Unabridged Dictionary (1913)

Membrane \Mem"brane\, n. [F., fr. L. membrana the skin that
   covers the separate members of the body, fr. L. membrum. See
   {Member}.] (Anat.)
   A thin layer or fold of tissue, usually supported by a
   fibrous network, serving to cover or line some part or organ,
   and often secreting or absorbing certain fluids.

   Note: The term is also often applied to the thin, expanded
         parts, of various texture, both in animals and
         vegetables.

   {Adventitious membrane}, a membrane connecting parts not
      usually connected, or of a different texture from the
      ordinary connection; as, the membrane of a cicatrix.

   {Jacob's membrane}. See under {Retina}.

   {Mucous membranes} (Anat.), the membranes lining passages and
      cavities which communicate with the exterior, as well as
      ducts and receptacles of secretion, and habitually
      secreting mucus.

   {Schneiderian membrane}. (Anat.) See {Schneiderian}.

   {Serous membranes} (Anat.), the membranes, like the
      peritoneum and pleura, which line, or lie in, cavities
      having no obvious outlet, and secrete a serous fluid.

Source : WordNet®

membrane
     n 1: a thin pliable sheet of material
     2: a pliable sheet of tissue that covers or lines or connects
        organs or cells of animals [syn: {tissue layer}]