Mū'cus, n.
n. [Lat.] (Physiol.) 1. A viscid fluid secreted by the mucous membrane, which it serves to moisten and defend. It covers the lining membranes of all the cavities which open externally, such as those of the mouth, nose, lungs, intestinal canal, urinary passages, and the like.
Sense 2. Hence, any other animal fluid of a viscid quality, as the synovial fluid, which lubricates the cavities of the joints; — improperly so used.