Source : Webster's Revised Unabridged Dictionary (1913)

Watchword \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.

Source : WordNet®

watchword
     n 1: a slogan used to rally support for a cause; "a cry to arms";
          "our watchword will be `democracy'" [syn: {war cry}, {rallying
          cry}, {battle cry}, {cry}]
     2: a secret word or phrase known only to a restricted group;
        "he forgot the password" [syn: {password}, {word}, {parole},
         {countersign}]