Why is a butter knife called a butter knife?

Butter knives have both edges and faces, and thus can be used both to slice pieces of butter, and then to spread them evenly on pieces of bread. In that sense, it is two machines in one. But wait, there's more! If you call now I'll also include this magnificent spoon at no extra cost! Yes, you can use it to eat soup without spilling it all over your shirt! Amaze your friends and relatives!