The term 'ERIE MULE' is a reference to the Erie Canal, which was an artificial waterway built in the early 19th century to connect the Great Lakes with the Hudson River. The canal was used to transport goods and people, and the mules that pulled the barges along the canal were known as 'Erie Mules'. The crossword solution for this term is 'SAL', which stands for 'Shipman's Assistant Laborer', the official title of the mule drivers who worked on the Erie Canal.