Source : Webster's Revised Unabridged Dictionary (1913)

Engineering \En`gi*neer"ing\, n.
   Originally, the art of managing engines; in its modern and
   extended sense, the art and science by which the mechanical
   properties of matter are made useful to man in structures and
   machines; the occupation and work of an engineer.

   Note: In a comprehensive sense, engineering includes
         architecture as a mechanical art, in distinction from
         architecture as a fine art. It was formerly divided
         into military engineering, which is the art of
         designing and constructing offensive and defensive
         works, and civil engineering, in a broad sense, as
         relating to other kinds of public works, machinery,
         etc.

   {Civil engineering}, in modern usage, is strictly the art of
      planning, laying out, and constructing fixed public works,
      such as railroads, highways, canals, aqueducts, water
      works, bridges, lighthouses, docks, embankments,
      breakwaters, dams, tunnels, etc.

   {Mechanical engineering} relates to machinery, such as steam
      engines, machine tools, mill work, etc.

   {Mining engineering} deals with the excavation and working of
      mines, and the extraction of metals from their ores, etc.
      Engineering is further divided into steam engineering, gas
      engineering, agricultural engineering, topographical
      engineering, electrical engineering, etc.

Mechanical \Me*chan"ic*al\, a. [From {Mechanic}, a.]
   1. Pertaining to, governed by, or in accordance with,
      mechanics, or the laws of motion; pertaining to the
      quantitative relations of force and matter, as
      distinguished from mental, vital, chemical, etc.; as,
      mechanical principles; a mechanical theory; mechanical
      deposits.

   2. Of or pertaining to a machine or to machinery or tools;
      made or formed by a machine or with tools; as, mechanical
      precision; mechanical products.

            We have also divers mechanical arts.  --Bacon.

   3. Done as if by a machine; uninfluenced by will or emotion;
      proceeding automatically, or by habit, without special
      intention or reflection; as, mechanical singing;
      mechanical verses; mechanical service.

   4. Made and operated by interaction of forces without a
      directing intelligence; as, a mechanical universe.

   5. Obtained by trial, by measurements, etc.; approximate;
      empirical. See the 2d Note under {Geometric}.

   {Mechanical effect}, effective power; useful work exerted, as
      by a machine, in a definite time.

   {Mechanical engineering}. See the Note under {Engineering}.
      

   {Mechanical maneuvers} (Mil.), the application of mechanical
      appliances to the mounting, dismounting, and moving of
      artillery. --Farrow.

   {Mechanical philosophy}, the principles of mechanics applied
      to the inverstigation of physical phenomena.

   {Mechanical powers}, certain simple instruments, such as the
      lever and its modifications (the wheel and axle and the
      pulley), the inclined plane with its modifications (the
      screw and the wedge), which convert a small force acting
      through a great space into a great force acting through a
      small space, or vice versa, and are used separately or in
      combination.

   {Mechanical solution} (Math.), a solution of a problem by any
      art or contrivance not strictly geometrical, as by means
      of the ruler and compasses, or other instruments.

Source : WordNet®

mechanical engineering
     n : the branch of engineering that deals with the design and
         construction and operation of machinery