Senescence (noun): the process of becoming old or biological aging. Senescence is inevitable for living things. At this time of year, we are able to enjoy "leaf senescence" as the green chlorophyll fades, revealing the yellow and orange pigments that were hidden in the leaf throughout the summer! Leaf senescence is important for a plant because it helps recycle nutrients (mostly nitrogen) back to the plant to store for next growing season.
Senescence can be traced back to Latin senex, meaning "old."