proposal of marriage vs marriage proposal

proposal of marriage and marriage proposal both are nouns.

Word	Noun	Adjective	Verb	Adverb
proposal of marriage	Yes	No	No	No
marriage proposal	Yes	No	No	No

As nouns, proposal of marriage and marriage proposal are synonyms defined as:

Other synonyms of proposal of marriage include marriage offer, proposal.

proposal of marriage (noun)	marriage proposal (noun)
an offer of marriage	an offer of marriage