the GNU version of the Collaborative International Dictionary of English
n. A form of articulation which admits of considerable motion; a complete joint; abarticulation. See articulation.
The Century Dictionary and Cyclopedia
n. In anatomy, that articulation of bones which leaves them free to move in some or any direction; free, as distinguished from fixed, arthrosis; thorough-joint: applied both to the joints themselves and to the motion resulting from such mechanism.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a joint so articulated as to move freely
Word Usage
"In a considerable part of their extent, especially in advanced life, they are separated by a space containing a synovia-like fluid, and hence the joint presents the characteristics of a diarthrosis."