"muddy, covered with clay," from Latin lutosus, from lutum "mud, dirt, mire, clay," from Proto-Italic *luto-, *lustro-, from PIE *l(h)u-to- "dirt," *l(h)u-(s)tro- "dirty place," from root *leu- "dirt; make dirty" (cognates: Greek lythron "gore, clotted blood," lyma "dirty water; moral filth, disgrace," lymax "rubbish, refuse," lyme "maltreatment, damage;" Latin lues "filth;" Old Irish loth "mud, dirt;" Welsh lludedic "muddy, slimy; Albanian lum "slime, mud;" Lithuanian liūtynas "loam pit").

Hence also English lute (n.) as a type of tenacious clay or cement used to stop holes, seal joints, etc. (c. 1400), from Old French lut or Medieval Latin lutum, from the Latin noun. Lute also was a verb in English.