The term 'Mammoth Trapper' refers to a person who uses TAR (3 letters) and tarpit (6 letters) to trap large animals such as mammoths. TAR is a sticky, black substance made from the distillation of coal, wood, or petroleum, while tarpit is a type of natural asphalt found in certain areas. The Mammoth Trapper would use these materials to create a sticky surface that would trap the animal, allowing them to be captured.