What is collective noun for banquet?

There isn't a specific, commonly used collective noun for a banquet.

You could use more general terms like:

* A gathering of guests at the banquet.

* A company of diners enjoying the banquet.

* A group of people attending the banquet.

If you want to be more descriptive, you could use phrases like:

* A throng of guests

* A bevy of diners

* A multitude of attendees

Ultimately, the best term to use depends on the specific context and the tone you want to convey.