A sign arranged or given to indicate a person; a word or material object employed to authenticate a person, message, or communication; a mark…

As a count noun (usually in singular). A watchword; a password. Now rare.

Military. A word or short phrase used as a password. Obsolete in technical use.

A sign or signal used in reply to another sign; spec. a private signal, usually a word, given or to be given to a soldier on guard by any one…

A password, watchword; a catchphrase. Obsolete. rare.

figurative. A distinguishing sign or token; a watchword, a password. (The earliest use in English.)

= countersign, n.

A selected word or phrase securing admission, recognition, etc., when used by those to whom it is disclosed; (Military) a watchword, a parole.

Chiefly colloquial. With the. Originally Irish English; later also Australian. A hint, a tip-off; a piece of inside information; a password. Now rare…

= sense 7.

a password or watchword.