ZIP vs ZIP code

ZIP and ZIP code both are nouns.

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

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

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

Other synonyms of ZIP include postal code, postcode.

ZIP (noun)	ZIP code (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