1. Being from 90 to 99 years old
   "the nonagenarian inhabitants of the nursing home"

1. Someone whose age is in the nineties
   "The nonagenarian celebrated her 95th birthday surrounded by four generations of family"

Derived forms: nonagenarians

See also: old

Type of: golden ager [N. Amer, informal], old person, oldster [N. Amer, informal], senior citizen