\Watch"word`\, n.
1. A word given to sentinels, and to such as have occasion to
   visit the guards, used as a signal by which a friend is
   known from an enemy, or a person who has a right to pass
   the watch from one who has not; a countersign; a password.
2. A sentiment or motto; esp., one used as a rallying cry or
   a signal for action.
         Nor deal in watchwords overmuch.      --Tennyson.