post card vs postal card

post card and postal card both are nouns.

Word	Noun	Adjective	Verb	Adverb
post card	Yes	No	No	No
postal card	Yes	No	No	No

As nouns, post card and postal card are synonyms defined as:

post card and postal card: a card for sending messages by post without an envelope

Other synonyms of post card include mailing-card, postcard.

post card (noun)	postal card (noun)
a card for sending messages by post without an envelope	a card for sending messages by post without an envelope