in·stroke (?n?str?k?)n. An inward stroke, especially a piston stroke moving away from the crankshaft.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.instroke (??n?str??k) nan inward stroke; esp in an engine, the stroke that moves the piston away from the crankshaftCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014