Source : Webster's Revised Unabridged Dictionary (1913)

Merestone \Mere"stone`\, n.
   A stone designating a limit or boundary; a landmark. --Bacon.

Source : WordNet®

merestone
     n : an old term for a landmark that consisted of a pile of
         stones surmounted by an upright slab [syn: {meerestone},
         {mearstone}]