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.

Atomic \A*tom"ic\, Atomical \A*tom"ic*al\, a. [Cf. F. atomique.]
   1. Of or pertaining to atoms.

   2. Extremely minute; tiny.

   {Atomic philosophy}, or {Doctrine of atoms}, a system which,
      assuming that atoms are endued with gravity and motion,
      accounted thus for the origin and formation of all things.
      This philosophy was first broached by Leucippus, was
      developed by Democritus, and afterward improved by
      Epicurus, and hence is sometimes denominated the Epicurean
      philosophy.

   {Atomic theory}, or the {Doctrine of definite proportions}
      (Chem.), teaches that chemical combinations take place
      between the supposed ultimate particles or atoms of
      bodies, in some simple ratio, as of one to one, two to
      three, or some other, always expressible in whole numbers.
      

   {Atomic weight} (Chem.), the weight of the atom of an element
      as compared with the weight of the atom of hydrogen, taken
      as a standard.

Source : WordNet®

atomic weight
     n : (chemistry) the ratio of the atomic mass of an element to
         half the atomic mass of carbon-12 [syn: {relative atomic
         mass}]