Protective secretion of the mucus membranes; in the gut it lubricates the passage of food and protects the epithelial cells; in the nose and throat and lungs it can make it difficult for bacteria to penetrate the body through the epithelium WordNet 3.0

Protective secretion of the mucous membranes; in the gut it lubricates the passage of food and protects the epithelial cells; in the nose and throat and lungs it can make it difficult for bacteria to penetrate the body through the epithelium Open English WordNet

Mucus is a slippery aqueous secretion produced by, and covering, mucous membranes. Wikipedia

Slippery secretion produced by, and covering, mucous membranes Wikipedia Disambiguation

(physiology) A viscous secretion from the lining of the mucous membranes. OmegaWiki

A slippery secretion from the lining of the mucous membranes. Wiktionary

Slippery secretion. Wiktionary (translation)