proposal of marriage vs marriage offer

proposal of marriage and marriage offer both are nouns.

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

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

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

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