engine

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 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'.