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Meaning of double-acting

dou•ble-act•ing

Pronunciation: (dub'ul ak'ting), [key]
— adj.
  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.