The word gammon goes back a long way, at least to the fourteenth century. It may have come into English from French, as the word jambon starts being used for ham in the middle-French dialects around the same time. Once gammon meant any rear haunch of a pig, or specifically the ham: later it came to mean some of the side cuts as well, though only as long as they were still attached to the pig's haunch while the meat was being cured. Today it simply means ham, and "gammon steak" is ham steak
