IN MORTUA MANU
in mortua manu (in mor-choo-<<schwa>> man-yoo), adj. & adv.[Law Latin “in a dead hand”] Hist. (Of property) perpetually controlled according to a decedent’s directions. • Land held by a religious society was described this way because the church could hold property perpetually without rendering feudal service. — Also termed in manu mortua. See DEADHAND CONTROL; MORTMAIN.
[Blacks Law 8th]