Use 'multitudinous' to describe something with a vast amount, emphasizing its abundance. She kept a multitudinous collection of books in her library.
Pro Tip 2/3
Not Countable
'Multitudinous' is used with things you can't count one by one, like stars or grains of sand. The beach had multitudinous grains of sand, impossible to count.
Pro Tip 3/3
Figuratively Speaking
Sometimes 'multitudinous' is used figuratively to express that something feels overwhelming. There were multitudinous thoughts running through my head during the interview.