Unity of Seisin Law and Legal Definition
Unity of seisin refers to the ownership of two plots of land by the same person. Seisin is a technical word meaning possession of an estate in land. The significance of unity of seisin is that when a person owns two properties which were formerly separately owned, any easements which enjoyed over the other are extinguished.
The rights are extinguished permanently, rather than simply lying dormant.
Unity of seisin is essential to a tenancy in common. [Hahn's Estate, 1941 Pa. Dist. & Cnty. Dec. LEXIS 397 (Pa. C.P. 1941)].