Pronunciation: (dub'ul ak'ting), [key]
1. (of a reciprocating engine, pump, etc.) having pistons accomplishing work in both directions, fluid being admitted alternately to opposite ends of the cylinders. Cf. single-acting.
2. (of a hinge of a door or the like) permitting movement in either direction from the normal, or closed, position.
3. having twice the usual effectiveness, strength, use, etc.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.