mucus

n. [ L. mucus, muccus; cf. mucere to be moldy or musty, Gr. my`xa mucus, and Skr. muc to release. Cf. Match for striking fire, Moist, Mucilage. ] 1. (Physiol.) A viscid fluid secreted by mucous membranes, which it serves to moisten and protect. It covers the lining membranes of all the cavities which open externally, such as those of the mouth, nose, lungs, intestinal canal, urinary passages, etc. [ 1913 Webster ]

2. (Physiol.) Any other animal fluid of a viscid quality, as the synovial fluid, which lubricates the cavities of the joints; -- improperly so used. [ 1913 Webster ]

3. (Bot.) A gelatinous or slimy substance found in certain algae and other plants. [ 1913 Webster ]