The Collaborative International Dictionary of English v.0.48:

Croupous \Croup"ous\ (kr??p"?s), a. (Med.)
   Relating to or resembling croup; especially, attended with
   the formation of a deposit or membrane like that found in
   membranous croup; as, croupous laryngitis.
   [1913 Webster]

   Croupous pneumonia, pneumonia attended with deposition of
      fibrinous matter in the air vesicles of the lungs;
      ordinary acute pneumonia.
      [1913 Webster]