1. coming after twelve others in a sequence; being number 13 in order

1. the thirteenth item in a series
2. one of thirteen equal parts of something

Examples

• Friday the thirteenth is considered unlucky by some people.
• She finished thirteenth in the race.
• The thirteenth chapter of the book was the most exciting.
• He was born on the thirteenth of May.
• Only a thirteenth of the students passed the difficult exam.
• The thirteenth floor was skipped in the building’s numbering.
• She celebrated her thirteenth birthday with a big party.