synovial fluid

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A viscous, nonnewtonian fluid found in the cavities of synovial joints, and whose main purpose is to reduce friction between the articular cartilage of synovial joints during movement.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun viscid lubricating fluid secreted by the membrane lining joints and tendon sheaths etc.