1776, coined in English with -an + Latin nonagenarius "containing ninety" (in Late Latin "someone ninety years old"), from nonagen "ninety each," related to nonaginta "the number ninety," from nonus "ninth" (see nones) + -genaria "ten times," from PIE *dkm-ta-, from *dekm- "ten" (see ten). As an adjective from 1893.