ninety-first adjective 1noun 1forms 1 adjective1 •The ordinal form of the number ninety-one, describing a person or thing in position number 91 of a sequence.The answer appears on the ninety-first page of the book.She finished ninety-first in the race. noun1 •One of ninety-one equal parts of a whole.A ninety-first of 1820 is 20. formsninety-firsts
