A guardsman is a soldier who is a member of a guard — one person in that group, not the group itself. In Britain it often means a soldier in the Guards, those famous regiments that once stood around the king or queen. You may picture the red coat and the tall black hat, though a guardsman is a real soldier, not only a tourist sight. Though actually, in the United States people also use guardsman for a member of the National Guard, which is a different kind of force, more like a reserve that a state can call on. The spelling with -man is an old army pattern; women serve too, but the traditional word has stayed. It is not a guardian. A guardian looks after a child in law. A guardsman is a soldier.