The Collaborative International Dictionary of English v.0.48:



   3. Importance, significance, dignity, etc; hence,
      seriousness; enormity; as, the gravity of an offense.
      [1913 Webster]

            They derive an importance from . . . the gravity of
            the place where they were uttered.    --Burke.
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   4. (Physics) The tendency of a mass of matter toward a center
      of attraction; esp., the tendency of a body toward the
      center of the earth; terrestrial gravitation.
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   5. (Mus.) Lowness of tone; -- opposed to acuteness.
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   Center of gravity See under Center.

   Gravity battery, See Battery, n., 4.

   Specific gravity, the ratio of the weight of a body to the
      weight of an equal volume of some other body taken as the
      standard or unit. This standard is usually water for
      solids and liquids, and air for gases. Thus, 19, the
      specific gravity of gold, expresses the fact that, bulk
      for bulk, gold is nineteen times as heavy as water.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

center \cen"ter\ (s[e^]n"t[~e]r), n. [F. centre, fr. L. centrum,
   fr. Gr. ke`ntron any sharp point, the point round which a
   circle is described, fr. kentei^n to prick, goad.]
   1. A point equally distant from the extremities of a line,
      figure, or body, or from all parts of the circumference of
      a circle; the middle point or place.
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   2. The middle or central portion of anything.
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   3. A principal or important point of concentration; the
      nucleus around which things are gathered or to which they
      tend; an object of attention, action, or force; as, a
      center of attaction.
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   4. The earth. [Obs.] --Shak.
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   5. Those members of a legislative assembly (as in France) who
      support the existing government. They sit in the middle of
      the legislative chamber, opposite the presiding officer,
      between the conservatives or monarchists, who sit on the
      right of the speaker, and the radicals or advanced
      republicans who occupy the seats on his left, See Right,
      and Left.
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   6. (Arch.) A temporary structure upon which the materials of
      a vault or arch are supported in position until the work
      becomes self-supporting.
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   7. (Mech.)
      (a) One of the two conical steel pins, in a lathe, etc.,
          upon which the work is held, and about which it
          revolves.
      (b) A conical recess, or indentation, in the end of a
          shaft or other work, to receive the point of a center,
          on which the work can turn, as in a lathe.
          [1913 Webster]

   Note: In a lathe the

   live center is in the spindle of the head stock; the

   dead center is on the tail stock.

   Planer centers are stocks carrying centers, when the object
      to be planed must be turned on its axis.
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   Center of an army, the body or troops occupying the place
      in the line between the wings.

   Center of a curve or Center of a surface (Geom.)
      (a) A point such that every line drawn through the point
          and terminated by the curve or surface is bisected at
          the point.
      (b) The fixed point of reference in polar coordinates. See
          Coordinates.

   Center of curvature of a curve (Geom.), the center of that
      circle which has at any given point of the curve closer
      contact with the curve than has any other circle whatever.
      See Circle.

   Center of a fleet, the division or column between the van
      and rear, or between the weather division and the lee.

   Center of gravity (Mech.), that point of a body about which
      all its parts can be balanced, or which being supported,
      the whole body will remain at rest, though acted upon by
      gravity.

   Center of gyration (Mech.), that point in a rotating body
      at which the whole mass might be concentrated
      (theoretically) without altering the resistance of the
      intertia of the body to angular acceleration or
      retardation.

   Center of inertia (Mech.), the center of gravity of a body
      or system of bodies.

   Center of motion, the point which remains at rest, while
      all the other parts of a body move round it.

   Center of oscillation, the point at which, if the whole
      matter of a suspended body were collected, the time of
      oscillation would be the same as it is in the actual form
      and state of the body.

   Center of percussion, that point in a body moving about a
      fixed axis at which it may strike an obstacle without
      communicating a shock to the axis.

   Center of pressure (Hydros.), that point in a surface
      pressed by a fluid, at which, if a force equal to the
      whole pressure and in the same line be applied in a
      contrary direction, it will balance or counteract the
      whole pressure of the fluid.
      [1913 Webster] Center

WordNet (r) 3.0 (2006):

center of gravity
    n 1: the point within something at which gravity can be
         considered to act; in uniform gravity it is equal to the
         center of mass [syn: center of gravity, centre of
         gravity]