letter box vs mailbox

letter box and mailbox both are nouns.

Word	Noun	Adjective	Verb	Adverb
letter box	Yes	No	No	No
mailbox	Yes	No	No	No

As nouns, letter box and mailbox are synonyms defined as:

As nouns, letter box and mailbox are synonyms defined as:

Other synonyms of letter box include postbox.

letter box (noun)	mailbox (noun)
a private box for delivery of mail	a private box for delivery of mail
public box for deposit of mail	public box for deposit of mail
a numbered compartment in a post office where mail is put to be called for