Definitions

1. noun

the person or thing that comes after the twelfth in a series, order, or position; thirteenth item or person

“She was the thirteenth guest to arrive at the party.”

2. adjective

being or coming after the twelfth in a series, order, or position

“The thirteenth chapter of the book was the most interesting part.”

3. adverb

to the thirteenth degree, or position

“He was extremely nervous, thirteenthly anxious about the exam.”