heat engine

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device that converts heat energy into work.

from The Century Dictionary.

• noun An engine which transforms heat into mechanical work.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun thermodynamics Any device which converts heat energy into mechanical work.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any engine that makes use of heat to do work