1) Demesne land; the land attached to a mansion (OED).
1420 ‘licence ... to enclose his ground from the land called the maynland behind the messuage’, York
1538 ther manour or graunge of Greatt Broughton and all arable laund, mayn, medowe, common of moore. Also used as an adjective: 1601 ‘one acre of mayne myddowe’, Moor Monkton. It survives in a number of minor place-names: 1588 Christopher Lowson of Munckton Maines, Ripon
1606 John Dodsworth of Massam Maynes.