Your query is a little unclear, David. Do you mean a word that groups collective nouns together?
E.g: A lexicon of collective nouns. <grin>
A collective noun (i.e. a noun that denotes a collection things) otherwise acts as a way of what I would call unitary grouping. That's just me.
Incidentally, there are plenty of other threads on collective nouns waiting behind the 'Search' button in the top right.