Twentieth means number 20 in a sequence or series. When you finish twentieth in a race, nineteen people crossed the finish line before you. If your birthday falls on the twentieth of the month, it comes after the nineteenth day and before the twenty-first.

The word also describes one of twenty equal parts of something. If you divide a pizza into twenty slices, each slice is one twentieth of the whole pizza. In fractions, one twentieth is written as 1/20.

You'll often see twentieth used with centuries. The twentieth century usually refers to the years 1901 through 2000, a period that saw dramatic changes like the invention of airplanes, computers, and the Internet. When historians talk about twentieth-century music or art, they mean works created during those hundred years.

The word follows the pattern of other ordinal numbers: first, second, third, and so on. Notice that while the counting number is “twenty,” the ordinal form changes to “twentieth,” just as “two” becomes “second” and “three” becomes “third.”