英語の（英国ベースの）貴賤結婚というのは
身分の違いの結婚によって
財産と地位の継承ができないって意味だって

dictionary.cambridge.org/dictionary/english/morganatic
morganatic
adjective
A morganatic marriage is one in which one partner is of higher social rank,
and the other cannot claim this partner's title or possessions or pass them to their children:
a morganatic marriage/union
the Archduke Franz Ferdinand's morganatic wife, Sophie Chotek