the thick, slimy secretion of the mucous membranes, that moistens and protects them
See mucus in American Heritage Dictionary 4
(myo͞oˈkəs)
noun
The viscous, slippery substance that consists chiefly of mucin, water, cells, and inorganic salts and is secreted as a protective lubricant coating by cells and glands of the mucous membranes.