The Collaborative International Dictionary of English v.0.48:

Membranous \Mem"bra*nous\, a. [Cf. F. membraneux.]
   1. Pertaining to, consisting of, or resembling, membrane; as,
      a membranous covering or lining.
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   2. (Bot.) Membranaceous.
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   Membranous croup (Med.), true croup. See Croup.
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The Collaborative International Dictionary of English v.0.48:

Croup \Croup\ (kr[=oo]p), n. [Scot. croup, cf. croup, crowp, to
   croak, to cry or speak with a hoarse voice; cf. also LG.
   kropp, G. kropf, the crop or craw of a bird, and tumor on the
   anterior part of the neck, a wen, etc. Cf. Crop.] (Med.)
   An inflammatory affection of the larynx or trachea,
   accompanied by a hoarse, ringing cough and stridulous,
   difficult breathing; esp., such an affection when associated
   with the development of a false membrane in the air passages
   (also called membranous croup). See False croup, under
   False, and Diphtheria.
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