position 15 in a countable series of things
"The fifteenth car to cross the finish line received a special medal for completing the marathon ahead of schedule."
The person or thing in the fifteenth position.
"The fifteenth runner crossed the finish line just seconds after the fourteenth."
The ordinal form of the number fifteen.
"She was born on the fifteenth day of June, exactly in the middle of her birth month."
The word fifteenth comes from Middle English and Old English, where it was formed by combining the number fifteen with a suffix meaning "th." Its original meaning simply indicated the ordinal position of the fifteenth item in a sequence.