senescent

adj

1. Growing old; decaying with the lapse of time.

   “And now, as the night was senescent / ⁠And star-dials pointed to morn— / ⁠As the star-dials hinted of morn— / At the end of our path a liquescent / ⁠And nebulous lustre was born”

   “The history of philosophic opinion itself in interpreted by Dr. Hall in terms of a similar development, in which immature adolescent systems, staid senescent and blasé philosophies have appeared and appealed to their public in direct relation to the status of the culture-periods in which they found origin and favor.”

   “Put all of this together and one can envision a world two generations hence in which the richer parts of Europe and the Pacific Rim are senescent walled cities, instability and authoritarian decay predominate across much of Eurasia, and real dynamism is sustained mostly in the parts of America that are growing and building at the moment[…]”

2. Characteristic of old age.
3. That ceases to divide.

   “When such lines and forms of organic development prevail, the individual, as the cell of the body, becomes soon senescent, drifting inevitably into age, decay, and death.”