From or evoking the 91st through 100th years of a century (chiefly the 1990s).

plural of ninety / The decade of the 1890s, 1990s, etc. / The decade of one's life from age 90 through age 99. / (temperature, rates, plural only) The range between 90 and 99.

Alternative letter-case form of nineties, in the context of a specific decade (almost always) the 1890s or 1990s.

The cardinal number occurring after eighty-nine and before ninety-one, represented in Roman numerals as XC and in Arabic numerals as 90.

(software engineering) A humorous aphorism stating that the first 90% of the code accounts for the first 90% of the development time, and the remaining 10% of the code accounts for the other 90% of the development time.

(cricket) The set of individual scores between 90 and 99, when a batsman may play badly due to feeling pressure to convert the score into a century.

(US) The decade of the 1890s, characterised by decadence, social scandal, and the beginning of the suffragette movement.

(UK) Synonym of Gay Nineties (the 1890s)

The cardinal number immediately following ninety-seven — ninety plus eight — and preceding ninety-nine.

The cardinal number immediately following ninety-three and preceding ninety-five.