a word that is popular in informal speech (usually for a short period)

motto

to add another signature to (a document) to give it authority

endorse

a short sentence or phrase used as a guide or rule of behaviour, as used by a school, club etc or expressed as a personal rule of conduct

saying, slogan

a secret word or phrase which enables a person to be recognized as a friend and not an enemy

secret word given for entry

a group of words (without a finite verb) forming part of sentence, e.g. 'in the garden', 'in order to', 'first of all'; to express something in words

group of words; way of speaking

an easily remembered phrase used to advertise something or to make clear the aim(s) of a group, campaign etc

motto