Source : Webster's Revised Unabridged Dictionary (1913)

Senescent \Se*nes"cent\, a. [L. senescent, p. pr. of senescere
   to grow old, incho. fr. senere to be old.]
   Growing old; decaying with the lapse of time. ``The night was
   senescent.'' --Poe. ``With too senescent air.'' --Lowell.

Source : WordNet®

senescent
     adj : growing old [syn: {aging}, {ageing}]