The phrase "most ecclesiastic" is typically used to describe something that is highly connected to the Christian church or its leaders. Synonyms for this term might include "most religious", "most devout", or "most pious". Other options could include "most spiritual", "most reverent", or "most holy". If you're looking for a more formal or technical synonym, you could try "most canonical" or "most theological". Ultimately, the best synonym for "most ecclesiastic" will depend on the context in which it is being used, as well as the speaker's intended meaning and tone.