late 14c., mussillage, "viscous substance found in vegetable material," from Old French mucilage (14c.), from Late Latin mucilago "musty or moldy juice" (4c.), from Latin mucere "be musty or moldy," from mucus "mucus" (see mucus). Meaning "adhesive" is first attested 1859.
mucilage mu·ci·lage (myōō'sə-lĭj)
A viscid preparation consisting of a solution of a plant-based gum in water and used in pharmacy as an excipient.