A plethora is an excessive amount of something that overwhelms with its abundance. If your teacher assigns a plethora of homework problems, you're getting an overwhelming pile that seems endless and far exceeds what you can reasonably handle. When a restaurant offers a plethora of menu choices, you might feel bewildered trying to pick just one meal from the dozens of options.

The word carries a sense of abundance that has crossed the line from “plenty” to “too much.” A library has many books, but a plethora of books would make it nearly impossible to find what you're looking for. You might hear someone say there's a plethora of evidence when investigators have collected far more proof than they actually need to solve a case.

People sometimes use plethora to simply mean “a lot,” but it traditionally suggests excess or overabundance. If you've got a plethora of ideas for your science project, you're bursting with so many possibilities that choosing one becomes its own challenge. The word often appears in more formal writing or speech, giving it a slightly sophisticated feel.