A noun refering to a person in his or her seventies, or a adjective refering to the state of being in one's seventies. Pronounced sep-tu-a-ja-nair-ian. Charles Bukowski wrote a book of poems called "Septuagenarian Stew."
"That poor old dog is so ancient it looks like a septuagenarian."
"My grandma is a septuagenarian. Her skin smells like mahogany and her eyes are full of tears."