octogenarian (n.)youdaoicibaDictYouDict[octogenarian 词源字典]
1789, with -an + French octogénaire "aged 80," from Latin octogenarius "containing eighty," from octogeni "eighty each," related to octoginta "eighty," from octo "eight" (see eight) + -genaria "ten times," from PIE *dkm-ta-, from *dekm- "ten" (see ten). As an adjective from 1784.[octogenarian etymology, octogenarian origin, 英语词源]