| n. pl. | 1. | The decade from 1890 to 1899; |
| 2. | The decade from 1990 to 1999; | |
| 3. | The time of life between ages 90 and 100. |
| Noun | 1. | nineties - the decade from 1890 to 1899 Synonyms: 1890s |
| 2. | nineties - the decade from 1990 to 1999 Synonyms: 1990s | |
| 3. | nineties - the time of life between 90 and 100 Synonyms: mid-nineties |