Definition of "thirty-first" in English

adjective

1. The ordinal form of the number thirty-one, describing a person or thing in position number 31 of a sequence.

   • The answer appears on the thirty-first page of the book.
   • She finished thirty-first in the race.

noun

1. One of thirty-one equal parts of a whole.

   • A thirty-first of 620 is 20.