marriage vs espousal

marriage and espousal both are nouns.

Word	Noun	Adjective	Verb	Adverb
marriage	Yes	No	No	No
espousal	Yes	No	No	No

As nouns, espousal is a hyponym of marriage; that is, espousal is a word with a more specific, narrower meaning than marriage:

Other hyponyms of marriage include bridal, civil marriage, love match, remarriage.

marriage (noun)	espousal (noun)
the act of marrying; the nuptial ceremony	the act of accepting with approval; favorable reception
two people who are married to each other	archaic terms for a wedding or wedding feast
the state of being a married couple voluntarily joined for life (or until divorce)	the act of becoming betrothed or engaged
a close and intimate union