Source : Webster's Revised Unabridged Dictionary (1913)

Sunset \Sun"set"\, Sunsetting \Sun"set`ting\, n.
   1. The descent of the sun below the horizon; also, the time
      when the sun sets; evening. Also used figuratively.

            'T is the sunset of life gives me mystical lore.
                                                  --Campbell.

   2. Hence, the region where the sun sets; the west.

   {Sunset shell} (Zo["o]l.), a West Indian marine bivalve
      ({Tellina radiata}) having a smooth shell marked with
      radiating bands of varied colors resembling those seen at
      sunset or before sunrise; -- called also {rising sun}.

Source : WordNet®

sunset
     adj 1: of a declining industry or technology; "sunset industries"
     2: providing for termination; "a program with a sunset
        provision" [syn: {sunset(a)}]
     n 1: the time in the evening at which the sun begins to fall
          below the horizon [syn: {sundown}] [ant: {dawn}]
     2: atmospheric phenomena accompanying the daily disappearance
        of the sun
     3: the daily event of the sun sinking below the horizon