In the law of estates. The peculiar characteristic of an estate held by several in joint tenancy, and which is fourfold, viz., unity of interest, unity of title, unity of time, and unity of possession. In other words, joint tenants have one and the same interest, accruing by one and the same conveyance, commencing at one and the same time, and held by one and the same undivided possession. 2 Bl. Comm. 180.