thirty-first adjective 1noun 1forms 1 adjective1 •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. noun1 •One of thirty-one equal parts of a whole.A thirty-first of 620 is 20. formsthirty-firsts
