a member of any of a number of nationalist churches rejecting various Roman Catholic tenets (esp. papal supremacy and papal infallibility) officially promulgated in relatively recent times: the churches were organized mainly in the late 19th cent.
See Old Catholic in American Heritage Dictionary 4
noun
A member of an independent religious organization formed by a group of German Roman Catholics who refused to accept the doctrine of papal infallibility proclaimed by the Vatican Council in 1870.