Wadset

[Scot. wad a pledge; akin to Sw. vad a wager. See Wed.]
(Scots Law) A kind of pledge or mortgage. [Written also wadsett.]

In Scotland, the ancient term for a mortgage.

A wadset is a right by which lands or other property are pledged by their owner to a creditor in security for a debt. It is usually in the form of a mutual contract, in which one party sells the land and the other grants the right of reversion.