matrimony, marry
姻 centers on the bond of marriage, specifically the formal union or matrimonial relationship.
姻 combines 女 (woman) with 因, which likely contributes both sound and the idea of a cause or reason, suggesting a woman becoming part of a family through marriage.
A woman 女 and a reason 因 come together: marriage is the reason a woman joins a new family.
For イン, imagine an inn where a wedding is held: inn -> イン, and the woman enters the inn to marry.
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marriage; matrimony
in-law; relative by marriage
relation by marriage
in-law; relative by marriage; relation by affinity
marriage acceptance certificate; certification that the local government office has received notification of a marriage
marriage registration
marriage registration
marriage procedures; procedure of marriage
marriage solemnizer; marriage celebrant
marriage laws
nuptial coloration (colouration)
certificate of legal capacity to contract marriage; certification of one's legal capacity to be married
legal age of marriage
marital relationship; marital relations