Nth \ENTH\, adjective:
1. Being the last in a series of infinitely decreasing or increasing values, amounts, etc.
2. (Of an item in a series of occurrences, planned events, things used, etc., that is thought of as being infinitely large) being the latest, or most recent.
Nth is the figurative use of the mathematical term indicating indefinite number, in which n is an abbreviation for number.
It was on the nth day of the nth month of the nth year, when Nina realized that she had reached the end of her life.