Hospitaller
noun
Hos·pi·tal·ler ˈhä-(ˌ)spi-tᵊl-ər 
variants or Hospitaler
: a member of a religious military order established in Jerusalem in the 12th century
Word History
Etymology
Middle English Hospiteler, Hospitaler, borrowed from Anglo-French Hospiteler, borrowed from Medieval Latin Hospitālārius, from Hospitāle, the Hospital of the Knights of St. John of Jerusalem (from hospitāle "residence for pilgrims and travelers") + Latin -ārius -ary entry 1 — more at hospital
First Known Use
14th century, in the meaning defined above