misalliance

An unsuitable alliance, especially in marriage.

A mésalliance.

An improper alliance or association; specifically, a marriage relation considered as degrading to one of the parties, owing to the inferior birth or standing of the other: in the latter sense often used in the French form, mésalliance.

A marriage with a person of inferior rank or social station; an improper alliance; a mesalliance.

An unsuitable alliance, especially an unsuitable marriage

an unsuitable alliance (especially with regard to marriage)