Nonagenarian \Non`a*ge*na"ri*an\, n. [L. nonagenarius containing, or consisting of, ninety, fr. nonageni ninety each; akin to novem nine.] A person ninety years old. web1913

nonagenarian adj : being from 90 to 99 years old; "the nonagenarian inhabitants of the nursing home" n : someone whose age is in the nineties wn