a very large amount of something
plethora - plenty
To have a 'plethora' of something means to have a copious amount of it to the point of excess. While it can be used to express an amount of something that is larger than you need, want, or can deal with, it is mostly used in a positive context to describe abundance.
After years of stagnation at the company, there has recently been a plethora of changes which have reinvigorated things.
There are a plethora of books on that subject, so finding information for your assignment should be easy.
The plethoric benefits of that vitamin make it an essential part of our everyday diet.