blow the gaff

present singular third person blows the gaff · participle present blowing the gaff · past blew the gaff · participle past blown the gaff

1. UKobsoleteslangTo disclose a secret.

   But, my child, if Geoffrey is to be got out at this immature stage it blows the gaff completely. Half of the crowd will vanish, including all the worst, and we shall have no proof at all of the real depths of the conspiracy.

   1934, Ernest Bramah [pseudonym; Ernest Brammah Smith], The Bravo of London

   Synonyms: let the cat out of the bag

2. UKobsoleteslangTo inform against a person.