noun

• (biology) The state or process of ageing, especially in humans; old age.
  "Organized shuffleboard has always filled me with dread. Everything about it suggests infirm senescence and death: it’s like it’s a game played on the skin of a void and the rasp of the sliding puck is the sound of that skin getting abraded away bit by bit."
• (cytology) Ceasing to divide by mitosis because of shortening of telomeres or excessive DNA damage.
  "2018, University of Edinburgh, "Liver Study Offers Insights into Hard-to-treat Diseases" (9 March 2018), Drug Discovery & Development. Tests in mice found that inducing senescence in bile duct cells - mimicking the process seen in human bile duct disease - led to liver scarring and damage of liver function."
• (gerontology) Old age; accumulated damage to macromolecules, cells, tissues and organs with the passage of time.
• (botany) Fruit senescence, leading to ripening of fruit.