A highwayman was a man who stopped people and carriages on the open road and robbed them, especially in Britain in the 1600s and 1700s. Highway here is the public road, and man is the person. He belongs to history and to stories: a rider at night, a pistol, the old shout to stand and hand over your money. Songs sometimes make him look bold or even polite, though actually he was a thief, and many were hanged. A very few women did the same work, but the old word is still highwayman. You would not use it for a thief in a car today; that is just a robber. This word lives on the old roads, in books and in films about the past.