Wiktionary
n. (context fractional English) One of ninety-one equal parts of a whole. num. (context ordinal English) The ordinal form of the number ninety-one, describing a person or thing in position number 91 of a sequence.
Usage examples of "ninety-first".
Bela Lincoln of Hingham and Ebenezer Storer, the treasurer of Harvard--and as Josiah noted, she and Adams were now both verging on their ninety-first year.
If you make the ninety-first cut of the apple pie, if you slice a carbon nucleus, you make not a smaller piece of carbon, but something else - an atom with completely different chemical properties.
The unearthly shape of Ninety-first Diplomat filled the image space on the holostage, which readjusted its scope to accommodate one more figure.
Bela Lincoln of Hingham and Ebenezer Storer, the treasurer of Harvard—and as Josiah noted, she and Adams were now both verging on their ninety-first year.