1) An open space, usually within a wood or forest.
1549 any playnes or cokglades within the seyd woodes, Bradley
1571 Thomas Smythe shall have a right of waye … to the towne … over the West Wood plaine, Ilkley
1636 as the same dothe lie in a plain called Coit Green, Fixby
1742 a spring wood and the plain ground in the same, Holmfirth. There is evidence that such open spaces might be deliberately created: 1752 William Tingle for paring and Stubbing a Plain in Tibnetherend Wood 10s 6d, Kirkheaton. The word was probably in use from the twelfth century at least, since charters contain references in Latin to ‘wood and plain’: c.1148 in bosco et in plano, Sawley. Used at times also for a space in the midst of houses that was open, free from obstructions: 1534-5 he used to sell in an open shop opening towards the market place or plain street, Pontefract
1642 as they come out of the Calf-howse ... all ditches and dales are plaine way, Elmswell.