What is "frank-marriage"

Frank-marriage \Frank"-mar"riage\, n. [Frank free + marriage.] (Eng. Law) A certain tenure in tail special; an estate of inheritance given to a man his wife (the wife being of the blood of the donor), and descendible to the heirs of their two bodies begotten. [Obs.]
--Blackstone.

n. (context obsolete UK legal English) A kind of estate tail.

Frank-marriage (liberum maritagium), in real property law, a species of estate tail, now obsolete.

When a man was seized of land in fee simple, and gave it to a daughter on marriage, the daughter and her husband were termed the donees in frank-marriage, because they held the land granted to them and the heirs of their two bodies free from all manner of service, except fealty, to the donor or his heirs until the fourth degree of consanguinity from the donor was passed.

This right of a freeholder so to give away his land at will was first recognized in the reign of Henry II, and became up to the reign of Elizabeth I the most usual kind of settlement.