nineties \nineties\ n. pl.

1. The decade from 1890 to 1899; as, the gay nineties. [WordNet 1.5]

2. The decade from 1990 to 1999; as, they spent a ton of money to solve the Y2K bug in the nineties. [WordNet 1.5]

3. The time of life between ages 90 and 100.

Syn: mid-nineties. [WordNet 1.5]

Source: The Collaborative International Dictionary of English v.0.48
 

Ninety \Nine"ty\, n.; pl. Nineties.

1. The sum of nine times ten; the number greater by a unit than eighty-nine; ninety units or objects. [1913 Webster]

2. A symbol representing ninety units, as 90 or xc. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

nineties

Source: WordNet (r) 2.0
 

Ninety \Nine"ty\, n.; pl. Nineties.

1. The sum of nine times ten; the number greater by a unit than eighty-nine; ninety units or objects.

2. A symbol representing ninety units, as 90 or xc.

Source: Webster's Revised Unabridged Dictionary (1913)