Emily Dickinson Lexicon

HOAR'STONE, n. [Arm. harz, a bound or limit. “In many parts of Great Britain are to be seen certain upright, rude pillars, or massive blocks of stone, which in England are called hoarstones, or by a name of nearly the same sound, with all the gradations of dialectical variety. Their appellation in Scotland is the Hare-stane.”]

A land-mark; a stone designating the bounds of an estate.