Noun letter box has 3 senses

• letter box(n = noun.artifact) call box, po box, pob, post-office box - a numbered compartment in a post office where mail is put to be called for; Array
is a kind of compartment

• letter box(n = noun.artifact) mailbox, postbox - public box for deposit of mail; Array
is a kind of maildrop
has particulars: pillar box

• letter box(n = noun.artifact) mailbox - a private box for delivery of mail; Array
is a kind of box