watchword

noun

Etymology: From Middle English wacche word, wacchworde, morphologically as watch (“guard, sentinel, sentry”) + word.

1. A word used as a motto, as expressive of a principle, belief, or rule of action; a rallying cry.

   “"How this perpetual gaiety," exclaimed Louis, "jars upon the ear! Good Heaven! is farewell to be said so gladly? I sometimes start when I think upon the hollowness of all that surrounds me. I often wish my eye had the power of searching the inmost depths of the bosoms whose watchword is my name."”

   “For-ward! be our watchword, Steps and voices joined; / Seek the things before us, Not a look behind.”

2. A prearranged reply to the challenge of a sentry or a guard; a password or signal by which friends can be known from enemies.

   “a Watchword sufficient for him that is wiſe”