ZIP code vs postcode

ZIP code and postcode both are nouns.

Word	Noun	Adjective	Verb	Adverb
ZIP code	Yes	No	No	No
postcode	Yes	No	No	No

As nouns, ZIP code and postcode are synonyms defined as:

ZIP code and postcode: a code of letters and digits added to a postal address to aid in the sorting of mail

Other synonyms of ZIP code include postal code, ZIP.

ZIP code (noun)	postcode (noun)
a code of letters and digits added to a postal address to aid in the sorting of mail	a code of letters and digits added to a postal address to aid in the sorting of mail