noundialect British, East Anglian English
Originally: dirt, refuse, dregs. Later: wet peaty soil; mortar or cement from old walls, especially used as manure.
Late Middle English; earliest use found in The Wars of Alexander. Origin uncertain; probably related to English regional (northern and midlands) morge, mudge mud, sludge; perhaps ultimately related to Old French, Middle French murgier, murgiere, murgiz, meurgier pile of stones, especially as resulting from extraction of stones from soil (13th–14th centuries; French regional murger, merger, morgier; compare post-classical Latin murgerium), perhaps itself a derivative of classical Latin mūrex in the extended sense ‘a sharp rock or stone’.