Source : Webster's Revised Unabridged Dictionary (1913)

Fallow \Fal"low\, a. [AS. fealu, fealo, pale yellow or red; akin
   to D. vaal fallow, faded, OHG. falo, G. falb, fahl, Icel.
   f["o]lr, and prob. to Lith. palvas, OSlav. plav[u^] white, L.
   pallidus pale, pallere to be pale, Gr. polio`s gray, Skr.
   palita. Cf. {Pale}, {Favel}, a., {Favor}.]
   1. Pale red or pale yellow; as, a fallow deer or greyhound.
      --Shak.

   2. [Cf. {Fallow}, n.] Left untilled or unsowed after plowing;
      uncultivated; as, fallow ground.

   {Fallow chat}, {Fallow finch} (Zo["o]l.), a small European
      bird, the wheatear ({Saxicola [oe]nanthe}). See
      {Wheatear}.

Fallow \Fal"low\, v. t. [imp. & p. p. {Fallowed}; p. pr. & vb.
   n. {Fallowing}.] [From {Fallow}, n.]
   To plow, harrow, and break up, as land, without seeding, for
   the purpose of destroying weeds and insects, and rendering it
   mellow; as, it is profitable to fallow cold, strong, clayey
   land.

Fallow \Fal"low\, n. [So called from the fallow, or somewhat
   yellow, color of naked ground; or perh. akin to E. felly, n.,
   cf. MHG. valgen to plow up, OHG. felga felly, harrow.]
   1. Plowed land. [Obs.]

            Who . . . pricketh his blind horse over the fallows.
                                                  --Chaucer.

   2. Land that has lain a year or more untilled or unseeded;
      land plowed without being sowed for the season.

            The plowing of fallows is a benefit to land.
                                                  --Mortimer.

   3. The plowing or tilling of land, without sowing it for a
      season; as, summer fallow, properly conducted, has ever
      been found a sure method of destroying weeds.

            Be a complete summer fallow, land is rendered tender
            and mellow. The fallow gives it a better tilth than
            can be given by a fallow crop.        --Sinclair.

   {Fallow crop}, the crop taken from a green fallow. [Eng.]

   {Green fallow}, fallow whereby land is rendered mellow and
      clean from weeds, by cultivating some green crop, as
      turnips, potatoes, etc. [Eng.]

Source : WordNet®

fallow
     adj 1: left unplowed and unseeded during a growing season; "fallow
            farmland"
     2: undeveloped but potentially useful; "a fallow gold market"

fallow
     n : cultivated land that is not seeded for one or more growing
         seasons