Merriam-Webster Collegiate Dictionary - ventricle

 noun  Etymology: Middle English, from Latin ventriculus, from diminutive of ventr-, venter belly  Date: 14th century a cavity of a bodily part or organ: as  a. a chamber of the heart which receives blood from a corresponding atrium and from which blood is forced into the arteries — see heart illustration  b. any of a system of communicating cavities in the brain that are continuous with the central canal of the spinal cord — see brain illustration