letter box let·ter·box uncommon noun 1. a numbered compartment in a post office where mail is put to be called for Synonymspost-office boxPOBcall boxletter box 2. public box for deposit of mail Synonymspostboxmailboxletter box 3. a private box for delivery of mail Synonymsmailboxletter box Related words Broader terms boxmaildropcompartment Narrower terms pillar box WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.
