In the feudal system, demesne (also spelled desmesne; pronounced [dih-MANE] or [dih-MEEN]; via Old French demeine from Latin dominium was all the land, not necessarily all contiguous to the castle, that was retained by a lord for his own use - as distinguished from land "alienated" or granted to others (alieni) as tenants either in freehold or leasehold.
