Source : Webster's Revised Unabridged Dictionary (1913)

Harvest \Har"vest\, n. [OE. harvest, hervest, AS. h[ae]rfest
   autumn; akin to LG. harfst, D. herfst, OHG. herbist, G.
   herbst, and prob. to L. carpere to pluck, Gr. ? fruit. Cf.
   {Carpet}.]
   1. The gathering of a crop of any kind; the ingathering of
      the crops; also, the season of gathering grain and fruits,
      late summer or early autumn.

            Seedtime and harvest . . . shall not cease. --Gen
                                                  viii. 22.

            At harvest, when corn is ripe.        --Tyndale.

   2. That which is reaped or ready to be reaped or gath??ed; a
      crop, as of grain (wheat, maize, etc.), or fruit.

            Put ye in the sickle, for the harvest is ripe.
                                                  --Joel iii.
                                                  13.

            To glean the broken ears after the man That the main
            harvest reaps.                        --Shak.

   3. The product or result of any exertion or labor; gain;
      reward.

            The pope's principal harvest was in the jubilee.
                                                  --Fuller.

            The harvest of a quiet eye.           --Wordsworth.

   {Harvest fish} (Zo["o]l.), a marine fish of the Southern
      United States ({Stromateus alepidotus}); -- called
      {whiting} in Virginia. Also applied to the dollar fish.

   {Harvest fly} (Zo["o]l.), an hemipterous insect of the genus
      {Cicada}, often called {locust}. See {Cicada}.

   {Harvest lord}, the head reaper at a harvest. [Obs.]
      --Tusser.

   {Harvest mite} (Zo["o]l.), a minute European mite ({Leptus
      autumnalis}), of a bright crimson color, which is
      troublesome by penetrating the skin of man and domestic
      animals; -- called also {harvest louse}, and {harvest
      bug}.

   {Harvest moon}, the moon near the full at the time of harvest
      in England, or about the autumnal equinox, when, by reason
      of the small angle that is made by the moon's orbit with
      the horizon, it rises nearly at the same hour for several
      days.

   {Harvest mouse} (Zo["o]l.), a very small European field mouse
      ({Mus minutus}). It builds a globular nest on the stems of
      wheat and other plants.

   {Harvest queen}, an image pepresenting Ceres, formerly
      carried about on the last day of harvest. --Milton.

   {Harvest spider}. (Zo["o]l.) See {Daddy longlegs}.

Source : WordNet®

harvest moon
     n : the full moon nearest the September equinox