Fifteenth means the item that comes in position number 15 in a sequence or list. If you line up all the students in your class by height, the fifteenth person is the one you count when you reach 15. If today is January 15th, it's the fifteenth day of the month.

The word can also mean one of fifteen equal parts of something. When you slice a pizza into fifteen pieces, each slice is one fifteenth of the whole pizza. If your soccer team has fifteen players and you need to know what fraction each player represents, the answer is one fifteenth (written as 1/15).

You'll see this word in dates all the time: “the fifteenth of March” or “March fifteenth.” Historical events often include it: the Fifteenth Amendment to the U.S. Constitution, ratified in 1870, prohibited denying citizens the right to vote based on race. When you're describing something's position or breaking things into equal parts, fifteenth gives you the precise language to be clear about exactly what you mean.