Noun | 1. | synovial fluid - viscid lubricating fluid secreted by the membrane lining joints and tendon sheaths etc. secretion - a functionally specialized substance (especially one that is not a waste) released from a gland or cell hyaluronic acid - a viscous mucopolysaccharide found in the connective tissue space and the synovial fluid of movable joints and the humors of the eye; a cementing and protective substance |