Catholic; Roman Catholic
Refers to Catholics, often in contrast with Protestants (新教徒). Used in historical or religious contexts.
He was raised as a Catholic.
The conflict between Catholics and Protestants has a long history.
カトリック is the more common modern term for 'Catholic'. 旧教徒 is a slightly older or more formal term.
Compound of 旧 (old) and 教徒 (believer, adherent of a religion), referring to the 'old' Christian denomination (Catholicism) as opposed to the 'new' Protestantism.