1. A condition in which a person is growing elderly without the usual signs of aging: Someone at the fitness studio guessed Sam's age to be in the 40s; however, because of his insenescence, he was actually in his 70s!

The conference speaker met a ninety-two-year old woman which he guessed to be about seventy, based on her energy as well as her appearance; however, he learned that there was a great discrepancy between her chronological age and her apparent biological insenescence.

2. The process of advancing in years, passing one's prime, or approaching old age: In the Oscar Wilde story, Dorion Gray, the main character fears insenescence and swore that he would always be young and handsome.

The university set up a department to study insenescence because there are many more people in the general population who are getting along in years.