This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. The state or process of ageing, especially in humans; old age.

n. Ceasing to divide by mitosis because of shortening of telomeres or excessive DNA damage.

n. Old age; accumulated damage to macromolecules, cells, tissues and organs with the passage of time.

n. Fruit senescence, leading to ripening of fruit.

n. The state of growing old; decay by time.

n. The condition of growing old, or of decaying by time; decadence.

n. the property characteristic of old age

n. the organic process of growing older and showing the effects of increasing age

"The gene is involved in senescence, a process that is thought to ensure that aging cells do not pass on harmful mutations."

oldness   

biological immortality   

senescent   

acquiescence    adolescence    coalescence    convalescence    essence    evanescence    luminescence    obsolescence    phosphorescence    quintessence   

dotage    tumorigenesis    recreancy    decrepitude    superannuation    dither    sexualization    gelation    alas!    doggrel