The Collaborative International Dictionary of English v.0.48:

Romanism \Ro"man*ism\, n.
   The tenets of the Church of Rome; the Roman Catholic
   religion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Romanism
    n 1: the beliefs and practices of the Catholic Church based in
         Rome [syn: Romanism, Roman Catholicism, papism]