watchword in WordNet English dictionary

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

watchword in Webster's English dictionary

1. A sentiment or motto; esp., one used as a rallying cry or a signal for action.
   
2. 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.
   

watchword in English Wiktionary