O.E. har "gray, venerable, old," the connecting notion being gray hair, from P.Gmc. *khairaz, from PIE *koi- "to shine." German retains the word as a title of respect, in Herr. Of frost, it is recorded in O.E. (hoar-frost is late 13c.), expressing the resemblance of the white feathers of frost to an old man's beard. Used as an attribute of boundary stones in O.E. (probably in ref. to being gray with lichens), hence common in place names.