Source : Webster's Revised Unabridged Dictionary (1913)

   7. A large quantity; a great number; as, a power o? good
      things. [Colloq.] --Richardson.

   8. (Mech.)
      (a) The rate at which mechanical energy is exerted or
          mechanical work performed, as by an engine or other
          machine, or an animal, working continuously; as, an
          engine of twenty horse power.

   Note: The English unit of power used most commonly is the
         horse power. See {Horse power}.
      (b) A mechanical agent; that from which useful mechanical
          energy is derived; as, water power; steam power; hand
          power, etc.
      (c) Applied force; force producing motion or pressure; as,
          the power applied at one and of a lever to lift a
          weight at the other end.

   Note: This use in mechanics, of power as a synonym for force,
         is improper and is becoming obsolete.
      (d) A machine acted upon by an animal, and serving as a
          motor to drive other machinery; as, a dog power.

   Note: Power is used adjectively, denoting, driven, or adapted
         to be driven, by machinery, and not actuated directly
         by the hand or foot; as, a power lathe; a power loom; a
         power press.

   9. (Math.) The product arising from the multiplication of a
      number into itself; as, a square is the second power, and
      a cube is third power, of a number.

   10. (Metaph.) Mental or moral ability to act; one of the
       faculties which are possessed by the mind or soul; as,
       the power of thinking, reasoning, judging, willing,
       fearing, hoping, etc. --I. Watts.

             The guiltiness of my mind, the sudden surprise of
             my powers, drove the grossness . . . into a
             received belief.                     --Shak.

   11. (Optics) The degree to which a lens, mirror, or any
       optical instrument, magnifies; in the telescope, and
       usually in the microscope, the number of times it
       multiplies, or augments, the apparent diameter of an
       object; sometimes, in microscopes, the number of times it
       multiplies the apparent surface.

   12. (Law) An authority enabling a person to dispose of an
       interest vested either in himself or in another person;
       ownership by appointment. --Wharton.

   13. Hence, vested authority to act in a given case; as, the
       business was referred to a committee with power.

   Note: Power may be predicated of inanimate agents, like the
         winds and waves, electricity and magnetism,
         gravitation, etc., or of animal and intelligent beings;
         and when predicated of these beings, it may indicate
         physical, mental, or moral ability or capacity.

   {Mechanical powers}. See under {Mechanical}.

   {Power loom}, or {Power press}. See Def. 8
       (d), note.

   {Power of attorney}. See under {Attorney}.

   {Power of a point} (relative to a given curve) (Geom.), the
      result of substituting the co["o]rdinates of any point in
      that expression which being put equal to zero forms the
      equation of the curve; as, x^{2} + y^{2} - 100 is the
      power of the point x, y, relative to the circle x^{2} +
      y^{2} - 100 = 0.

Source : WordNet®

power of attorney
     n : a legal instrument authorizing someone to act as the
         grantor's agent