The Collaborative International Dictionary of English v.0.48:
Merestone \Mere"stone`\, n. A stone designating a limit or boundary; a landmark. --Bacon. [1913 Webster]WordNet (r) 3.0 (2006):
merestone n 1: an old term for a landmark that consisted of a pile of stones surmounted by an upright slab [syn: merestone, meerestone, mearstone]