Source : Webster's Revised Unabridged Dictionary (1913)

Weight \Weight\, n. [OE. weght, wight, AS. gewiht; akin to D.
   gewigt, G. gewicht, Icel. v[ae]tt, Sw. vigt, Dan. v[ae]gt.
   See {Weigh}, v. t.]
   1. The quality of being heavy; that property of bodies by
      which they tend toward the center of the earth; the effect
      of gravitative force, especially when expressed in certain
      units or standards, as pounds, grams, etc.

   Note: Weight differs from gravity in being the effect of
         gravity, or the downward pressure of a body under the
         influence of gravity; hence, it constitutes a measure
         of the force of gravity, and being the resultant of all
         the forces exerted by gravity upon the different
         particles of the body, it is proportional to the
         quantity of matter in the body.

   2. The quantity of heaviness; comparative tendency to the
      center of the earth; the quantity of matter as estimated
      by the balance, or expressed numerically with reference to
      some standard unit; as, a mass of stone having the weight
      of five hundred pounds.

            For sorrow, like a heavy-hanging bell, Once set on
            ringing, with his own weight goes.    --Shak.

   3. Hence, pressure; burden; as, the weight of care or
      business. ``The weight of this said time.'' --Shak.

            For the public all this weight he bears. --Milton.

            [He] who singly bore the world's sad weight.
                                                  --Keble.

   4. Importance; power; influence; efficacy; consequence;
      moment; impressiveness; as, a consideration of vast
      weight.

            In such a point of weight, so near mine honor.
                                                  --Shak.

   5. A scale, or graduated standard, of heaviness; a mode of
      estimating weight; as, avoirdupois weight; troy weight;
      apothecaries' weight.

   6. A ponderous mass; something heavy; as, a clock weight; a
      paper weight.

            A man leapeth better with weights in his hands.
                                                  --Bacon.

   7. A definite mass of iron, lead, brass, or other metal, to
      be used for ascertaining the weight of other bodies; as,
      an ounce weight.

   8. (Mech.) The resistance against which a machine acts, as
      opposed to the power which moves it. [Obs.]

   {Atomic weight}. (Chem.) See under {Atomic}, and cf.
      {Element}.

   {Dead weight}, {Feather weight}, {Heavy weight}, {Light
   weight}, etc. See under {Dead}, {Feather}, etc.

   {Weight of observation} (Astron. & Physics), a number
      expressing the most probable relative value of each
      observation in determining the result of a series of
      observations of the same kind.

   Syn: Ponderousness; gravity; heaviness; pressure; burden;
        load; importance; power; influence; efficacy;
        consequence; moment; impressiveness.



   {Dead plate} (Mach.), a solid covering over a part of a fire
      grate, to prevent the entrance of air through that part.
      

   {Dead pledge}, a mortgage. See {Mortgage}.

   {Dead point}. (Mach.) See {Dead center}.

   {Dead reckoning} (Naut.), the method of determining the place
      of a ship from a record kept of the courses sailed as
      given by compass, and the distance made on each course as
      found by log, with allowance for leeway, etc., without the
      aid of celestial observations.

   {Dead rise}, the transverse upward curvature of a vessel's
      floor.

   {Dead rising}, an elliptical line drawn on the sheer plan to
      determine the sweep of the floorheads throughout the
      ship's length.

   {Dead-Sea apple}. See under {Apple}.

   {Dead set}. See under {Set}.

   {Dead shot}.
       (a) An unerring marksman.
       (b) A shot certain to be made.

   {Dead smooth}, the finest cut made; -- said of files.

   {Dead wall} (Arch.), a blank wall unbroken by windows or
      other openings.

   {Dead water} (Naut.), the eddy water closing in under a
      ship's stern when sailing.

   {Dead weight}.
       (a) A heavy or oppressive burden. --Dryden.
       (b) (Shipping) A ship's lading, when it consists of heavy
           goods; or, the heaviest part of a ship's cargo.
       (c) (Railroad) The weight of rolling stock, the live
           weight being the load. --Knight.

   {Dead wind} (Naut.), a wind directly ahead, or opposed to the
      ship's course.

   {To be dead}, to die. [Obs.]

            I deme thee, thou must algate be dead. --Chaucer.

   Syn: Inanimate; deceased; extinct. See {Lifeless}.

Source : WordNet®

dead weight
     n 1: an oppressive encumbrance
     2: a heavy motionless weight