Anything multitudinous is countless, infinite, innumerable, and, myriad: you couldn't count it if you tried.
This is a fancy way to describe more than a whole lot of something — so many, in fact, that you could never count them all. There are multitudinous atoms in your body, multitudinous drops in the ocean, and multitudinous grains of sand on the beach. The number of books in the library isn't multitudinous, even though it would take forever to count them all. Save multitudinous for things that are so amazingly numerous that counting is useless.