Interchurch is a term commonly used to refer to activities or events that involve two or more churches. However, there are several synonyms you can use to express the same idea depending on the context. For instance, you could use the word "ecumenical" to describe an event where different churches work together to accomplish a common goal. Another synonym for interchurch could be "interdenominational," which refers to activities that involve different denominations within Christianity. "Interfaith" is another term you could use to describe events where different religions come together. In short, choosing the right synonym for interchurch will depend on the context and the specific meaning you want to convey.