postman's knock

postman's knock

1. (uncountable) Synonym of post office (“a party game involving the exchange of kisses”).
2. (countable) A double knock at the door to indicate the delivery of letters or telegrams.
   • 1897, Bram Stoker, Dracula, New York, N.Y.: Modern Library, →OCLC:

     Whilst he was speaking we were startled by a knock at the hall door, the double postman's knock of the telegraph boy.