The word "muscle" comes from the Latin word musculus, which literally translates to “a little mouse.” Why? It was once thought that the shape and movement of some human muscles, especially the biceps, resembled mice moving under the skin. This is also reflected in the Greek word mys, which means both "mouse" and "muscle.” A similar phenomenon can be seen in the Old Church Slavonic terms mysi ("mouse") and mysica ("arm”); the German term maus ("mouse; muscle"); the Arabic terms 'adalah ("muscle") and 'adal ("field mouse"); and the Cornish term logodenfer ("calf of the leg," – or more literally, "mouse of the leg"). The word muscle as an English noun came into usage in the late 14th century, but the verb form didn’t enter common usage until 1913. By 1929 it was part of U.S. underworld slang, and in 1969, it was applied to describe a certain type of car (“muscle car”).