: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'.
-- The AI Hackers Dictionary
