ninetyfirst

Ninetyfirst is the ordinal form corresponding to the cardinal ninety-one, used to indicate position in a sequence. In standard English, the conventional written form is ninety-first; ninetyfirst is nonstandard and may appear as a misprint or in stylized branding, toys with typography, or in software identifiers where spaces or hyphens are avoided.

In numerals, the ordinal is written as 91st. When spelled out, it is typically written with a hyphen as ninety-first, since it is a compound adjective modifying a noun (for example, the ninety-first chapter). The hyphen helps clarify that the two words function together as a single descriptor.

The formation follows English ordinal rules for numbers ending in 1, with an exception pattern for the teens: the suffix is -st (as in first, twenty-first, ninety-first) because the tens digit is not 1. Thus ninety-first is correct in full, while ninetyfirst is usually considered nonstandard in formal writing.

Applications of the term appear in lists, rankings, dates, and ordinal designations. It also occurs in phrases like the ninety-first percentile or the ninety-first day of the year, where the hyphenated form is used to join the ordinal with the following noun or noun phrase.

See also: first, twenty-first, ninety-second, ordinal numbers.