twenty-first

twenty-first (not comparable)

1. The ordinal form of the number twenty-one.

21st, 21^st, XXI

twenty-first (plural twenty-firsts)

1. The person or thing in the twenty-first position.
2. One of twenty-one equal parts of a whole, usually written ¹⁄₂₁.
3. (informal) A party to celebrate a twenty-first birthday.

• (nonstandard, humorous) twenty-oneth

• previous: twentieth, next: twenty-second