Meaning of opposed-piston engine

op•posed'-pis'ton en"gine

Pronunciation: (u-pōzd'pis'tun), [key]
  1. a reciprocating engine, as a diesel engine, in which each cylinder has two pistons that move simultaneously away from or toward the center.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.