Meaning of contractile vacuole

contrac'tile vac"uole

Pronunciation: [key]
— Cell Biol. Cell Biol.
  1. a membrane-enveloped cellular organelle, found in many microorganisms, that periodically expands, filling with water, and then contracts, expelling its contents to the cell exterior: thought to be important in maintaining hydrostatic equilibrium. See diags. under
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.