SEISIN, in Law, signifies possession. In this sense we say, premier seisin, for the first possession, &c.
Seisin is divided into that in deed or in fact, and that in law. A seisin in deed is where a possession is actually taken: but a seisin in law is, where lands descend, and the party has not entered thereon; or, in other words, it is where a person has a right to lands, &c. and is by wrong disseised of them. A seisin in law is held to be sufficient to avow on; though to the bringing of an assize, actual seisin is required; and where seisin is alleged, the person pleading it must show of what estate he is seised, &c.
Seisin of a superior service is deemed to be a seisin of all superior and casual services that are incident thereto; and seisin of a lessee for years, is sufficient for him in reversion.