Source : Webster's Revised Unabridged Dictionary (1913)

Metacenter \Met`a*cen"ter\or -tre \-tre\, n. [Pref. meta- +
   center.] (Hydrostatics)
   The point of intersection of a vertical line through the
   center of gravity of the fluid displaced by a floating body
   which is tipped through a small angle from its position of
   equilibrium, and the inclined line which was vertical through
   the center of gravity of the body when in equilibrium.

   Note: When the metacenter is above the center of gravity, the
         position of the body is stable; when below it,
         unstable.

Source : WordNet®

metacenter
     n : (shipbuilding) the point of intersection between two
         vertical lines, one line through the center of buoyancy
         of the hull of a ship in equilibrium and the other line
         through the center of buoyancy of the hull when the ship
         is inclined to one side; the distance of this
         intersection above the center of gravity is an indication
         of the stability of the ship [syn: {metacentre}]