An antonym for schism is

Answer 1

It's the Union - act, when schismatic part of church express it's willnes to return to universal church. One example of such unions (the one that i remember right now) is Union in Brzesc (Border of Poland and Belarus, Europe). In 1595 part of orthodox church have returned to unity with catholic church after Great Eastern Schism (1054) Rest of orthodox church still doesn't live in full unity with Roman Catholic Church, but there are carufull tries to achieve such a state.