thirty-first

thirty-first

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.

English ordinal numbers may function as either an adjective or as a noun, and almost never appear in the plural.

• 31st, 31^st

thirty-first (plural thirty-firsts)

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

   A thirty-first of 620 is 20.

• thirty-oneth