And now, how are going to get to an "agreed upon definition of denomination". Who is going to be the final authority in a question this serious? Perhaps we should just convene a council or ten and decide through the years what "denomination" means. But first we would need to decide if we are fallible or infallible. Because if we are not infallible, then who is going to trust our final answer? It just gets so complicated...
Working definitions are useful because they establish that when one party says "X" they mean."Y", or "Z". No one has to agree that that is the "right" definition, but it facilitates communications.
So to start this off, when Catholics say "Denomination" they are referring to a religious group that shares a unique authority. Within the Roman See we recognize that authority is the Pope. What is YOUR definition of "denomination"?
Not all Catholics agree on everything, but we must agree on that or we are not in communication with the Roman See. Those who don't, like the SSPX are receive latae sententiae excommunication by their own actions.