The Collaborative International Dictionary of English v.0.48:

Engine \En"gine\ ([e^]n"j[i^]n), n. [F. engin skill, machine,
   engine, L. ingenium natural capacity, invention; in in + the
   root of gignere to produce. See Genius, and cf.
   Ingenious, Gin a snare.]
   1.

   Note: (Pronounced, in this sense, [e^]n*j[=e]n".) Natural
         capacity; ability; skill. [Obs.]
         [1913 Webster]

               A man hath sapiences three,
               Memory, engine, and intellect also. --Chaucer.
         [1913 Webster]

   2. Anything used to effect a purpose; any device or
      contrivance; a machine; an agent. --Shak.
      [1913 Webster]

            You see the ways the fisherman doth take
            To catch the fish; what engines doth he make?
                                                  --Bunyan.
      [1913 Webster]

            Their promises, enticements, oaths, tokens, and all
            these engines of lust.                --Shak.
      [1913 Webster]

   3. Any instrument by which any effect is produced;
      especially, an instrument or machine of war or torture.
      "Terrible engines of death." --Sir W. Raleigh.
      [1913 Webster]

   4. (Mach.) A compound machine by which any physical power is
      applied to produce a given physical effect.
      [1913 Webster]

   Engine driver, one who manages an engine; specifically, the
      engineer of a locomotive.

   Engine lathe. (Mach.) See under Lathe.

   Engine tool, a machine tool. --J. Whitworth.

   Engine turning (Fine Arts), a method of ornamentation by
      means of a rose engine.
      [1913 Webster]

   Note: The term engine is more commonly applied to massive
         machines, or to those giving power, or which produce
         some difficult result. Engines, as motors, are
         distinguished according to the source of power, as
         steam engine, air engine, electro-magnetic engine; or
         the purpose on account of which the power is applied,
         as fire engine, pumping engine, locomotive engine; or
         some peculiarity of construction or operation, as
         single-acting or double-acting engine, high-pressure or
         low-pressure engine, condensing engine, etc.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Engine \En"gine\, v. t.
   1. To assault with an engine. [Obs.]
      [1913 Webster]

            To engine and batter our walls.       --T. Adams.
      [1913 Webster]

   2. To equip with an engine; -- said especially of steam
      vessels; as, vessels are often built by one firm and
      engined by another.
      [1913 Webster]

   3. (Pronounced, in this sense, ?????.) To rack; to torture.
      [Obs.] --Chaucer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

engine
    n 1: motor that converts thermal energy to mechanical work
    2: something used to achieve a purpose; "an engine of change"
    3: a wheeled vehicle consisting of a self-propelled engine that
       is used to draw trains along railway tracks [syn:
       locomotive, engine, locomotive engine, railway
       locomotive]
    4: an instrument or machine that is used in warfare, such as a
       battering ram, catapult, artillery piece, etc.; "medieval
       engines of war"

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "engine":
   AC motor, Corliss engine, Otto engine, Wankel engine, aeromotor,
   air engine, alembic, anvil, apparatus, appliance, arc-jet engine,
   axial-flow turbojet, beam engine, bearings, blowing engine, boiler,
   caldron, cam, cam engine, camshaft, capacitor motor,
   commutator motor, compensated motor, compound motor,
   condensing engine, connecting rod, convenience, crankcase,
   crankshaft, crucible, cylinder, cylinder head, diagonal engine,
   differential, direct-acting engine, donkey engine, drive, dynamo,
   dynamotor, electric motor, enginery, facility, fire engine,
   fixture, flywheel, gas jet, gas turbine engine, gearbox, gears,
   generator, hot-air engine, hydraulic engine, hydro-jet,
   impulse duct engine, inverted engine, ion engine, ion rocket, jet,
   lathe, locomotive, machine, machinery, mechanical aid,
   mechanical device, mechanism, melting pot, mortar, motive power,
   motor, outboard motor, pancake engine, piston, piston engine,
   piston rod, piston-valve engine, plasma engine, portable engine,
   power plant, power source, propeller-jet engine, propjet,
   pulse-jet engine, pumping engine, radial engine, ramjet,
   ramjet engine, reciprocating engine, refrigerating engine,
   resojet engine, retort, rocket engine, rocket motor, rotary engine,
   rotary-piston engine, rotor motor, servomotor, shunt motor,
   steam engine, supercharged engine, synchronous motor, test tube,
   three-phase motor, traction engine, transducer, transformer,
   transmission, turbine, turbojet, turbojet engine, turboprop,
   utility, variable-speed motor, vernier engine, vertical engine



The Jargon File (version 4.4.7, 29 Dec 2003):

engine
 n.

    1. A piece of hardware that encapsulates some function but can't be used
    without some kind of front end. Today we have, especially, print engine:
    the guts of a laser printer.

    2. An analogous piece of software; notionally, one that does a lot of noisy
    crunching, such as a database engine.

    The hacker senses of engine are actually close to its original,
    pre-Industrial-Revolution sense of a skill, clever device, or instrument
    (the word is cognate to ?ingenuity?). This sense had not been completely
    eclipsed by the modern connotation of power-transducing machinery in
    Charles Babbage's time, which explains why he named the stored-program
    computer that he designed in 1844 the Analytical Engine.


The Free On-line Dictionary of Computing (30 December 2018):

engine

    1. A piece of hardware that encapsulates some
   function but can't be used without some kind of front end.
   Today we have, especially, "print engine": the guts of a
   laser printer.

   2. An analogous piece of software; notionally, one that does a
   lot of noisy crunching, such as a "database engine", or
   "search engine".

   The hackish senses of "engine" are actually close to its
   original, pre-Industrial-Revolution sense of a skill, clever
   device, or instrument (the word is cognate to "ingenuity").
   This sense had not been completely eclipsed by the modern
   connotation of power-transducing machinery in Charles
   Babbage's time, which explains why he named the
   stored-program computer that he designed in 1844 the
   "Analytical Engine".

   [Jargon File]

   (1996-05-31)