The ordinal form of the number ninety-nine, describing a person or thing in position number 99 of a sequence.(noun)
One of ninety-nine equal parts of a whole.(noun)
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Use "ninety-ninth" in a sentence
"I live in an apartment on the ninety-ninth floor of my block"
"The question became insistent almost as soon as he entered the US Senate in 2005, though he was then only ninety-ninth in seniority."
"People in the ninety-fifth to the ninety-ninth percentiles of income have represented a fairly constant share of the national income for twenty-five years now."