merestone

mere-,墙，词源同mural,intramural,stone,石头。即当做墙的石头，引申词义界碑，界石。

merestone (n.)

"stone serving as a landmark," Old English mærstan "boundary stone," from mære "boundary, object indicating a boundary," from Proto-Germanic *mairjo- (cognates: Middle Dutch mere "boundary mark, stake," Old Norse -mæri "boundary, border-land"), related to Latin murus "wall" (see mural). Hence also meresman "man appointed to find boundaries" (of a parish, etc.).