WordReference Random House Unabridged Dictionary of American English © 2026
contrac′tile vac′uole, [Cell Biol.]
- 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 ameba, paramecium.
- 1875–80