Senescence
Etymology
From Latin "senescere" (to grow old), from "senex" (old man) — the same root behind "senior" and "senate." It names aging as an active biological trajectory rather than mere elapsed time. "Cellular senescence" is a modern refinement for cells that permanently cease dividing.
noun · /sih-NES-ence/
The process of biological aging and gradual deterioration of function over time.
What it names
The precise scientific word for aging as a process — useful both at the scale of an organism growing old and, in "cellular senescence," for individual cells that stop dividing yet linger and drive age-related decline.
Example
A whole field of research now targets cellular senescence, hoping to clear the worn-out cells that accelerate the body’s decline.
Related idea
Compare moribund (already here), which means near death or obsolescence; senescence is the long slope of aging itself, not the final approach to an end.