Definitions

1. noun

The number 15 or a person or thing that is 15 years old.

“She celebrated her fifteenth birthday last night.”

2. adjective

Relating to or consisting of fifteen people or things.

“The fifteen-man team won the championship.”

3. adverb

In a way that is typical of a person or thing that is 15 years old.

“He walked with a fifteenth-year-old swagger.”