Formal:
* Clergy - This is the most common and straightforward term.
* Convocation - This is often used for a formal gathering of clergy.
* Synod - This refers to a council or assembly of clergy, especially in the context of a church or religious denomination.
Informal:
* Body - This can be used to refer to a group of clergy, especially when discussing their collective opinion or actions.
* Gathering - This is a more general term, suitable for any group of clergy meeting together.
The best choice will depend on the specific context and the desired level of formality.