PO Box vs Post-Office box

PO Box and Post-Office box both are nouns.

Word	Noun	Adjective	Verb	Adverb
PO Box	Yes	No	No	No
Post-Office box	Yes	No	No	No

As nouns, PO Box and Post-Office box are synonyms defined as:

PO Box and Post-Office box: a numbered compartment in a post office where mail is put to be called for

Other synonyms of PO Box include call box, letter box, POB.

PO Box (noun)	Post-Office box (noun)
a numbered compartment in a post office where mail is put to be called for	a numbered compartment in a post office where mail is put to be called for