Plethora means an abundance or excess of something. If you have 15 different people who want to take you on a date, you have a plethora of romantic possibilities. Plethora comes from the Greek for fullness.. Although it was originally used only in old-fashioned medicine to describe the condition of having too much blood, we use it to talk about any excessive supply. If you run a theater and all the seats are taken, that's a full house.