SEISIN, in Law, signifies possession. In this sense we say, premier seisin, for the first possession. 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 it is where a person has a right to lands, 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.