instroke

from WordNet (r) 3.0 (2006)

instroke
    n 1: the stroke of an engine piston moving away from the
         crankshaft

from The Collaborative International Dictionary of English v.0.48

Instroke \In"stroke`\, n.
   An inward stroke; specif., in a steam or other engine, a
   stroke in which the piston is moving away from the crank
   shaft; -- opposed to {outstroke}.
   [Webster 1913 Suppl.]