Source : Webster's Revised Unabridged Dictionary (1913)

Membranous \Mem"bra*nous\, a. [Cf. F. membraneux.]
   1. Pertaining to, consisting of, or resembling, membrane; as,
      a membranous covering or lining.

   2. (Bot.) Membranaceous.

   {Membranous croup} (Med.), true croup. See {Croup}.

Source : WordNet®

membranous
     adj 1: relating to or made of or similar to a membrane; "membranous
            lining"
     2: characterized by formation of a membrane (or something
        resembling a membrane); "membranous gastritis" [syn: {membrane-forming}]