Formal:
* Legislature: This is the most common and formal term, referring to the body of lawmakers as a whole.
* Parliament: This is another formal term, typically used in countries with parliamentary systems.
* Congress: This is a formal term used specifically in the United States.
Informal:
* Assembly: This term suggests a gathering of lawmakers for a specific purpose.
* Body: This is a general term that can be used to refer to any group of people, including lawmakers.
* Group: This is another general term that can be used for any collection of individuals.
More specific:
* Senate: This refers to the upper house of a bicameral legislature.
* House: This refers to the lower house of a bicameral legislature.
The best collective noun to use will depend on the specific context and the desired level of formality.