SUMPTER, a pack-horse or mule, a beast for carrying burdens, particularly for military purposes. There were two words once in use, which in sense, if not in form, have coalesced. These are " sommer " or " summer " and " sumpter." The first comes through the Old French sommier, a pack-horse, the other through sommetier, a pack-horse driver. Both come ultimately from Late Lat. salma, from sagma, a pack, burden, Old French somme, saume; Greek cay pa, burden, (r&TTfiv, to load. " Sumpter " in the sense of a driver of a pack-horse is rare, and the word is always joined with another explanatory word.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)