The Collaborative International Dictionary of English v.0.48:

Hospitaler \Hos"pi*tal*er\, n. [Written also hospitaller.] [F.
   hospitalier. See Hospital, and cf. Hostler.]
   1. One residing in a hospital, for the purpose of receiving
      the poor, the sick, and strangers.
      [1913 Webster]

   2. One of an order of knights who built a hospital at
      Jerusalem for pilgrims, A. D. 1042. They were called
      Knights of St. John of Jerusalem, and after the removal of
      the order to Malta, Knights of Malta.
      [1913 Webster] hospitalisation