endearing term for a baby, a girl, etc., c.1600, from Middle English moppe "little child, baby doll" (mid-15c.) + -et, diminutive suffix. The Middle English word also meant "simpleton, fool," and may have been cognate with Low German mop "simpleton" [Barnhart]. Or, if "baby doll" is the original sense in Middle English, perhaps from Latin mappa "napkin, tablecloth," hence "rag doll."