Old English har "hoary, gray, venerable, old," the connecting notion being gray hair, from Proto-Germanic *haira (source also of Old Norse harr "gray-haired, old," Old Saxon, Old High German her "distinguished, noble, glorious," German hehr), from PIE *kei- (2), source of color adjectives (see hue (n.1)). German also uses the word as a title of respect, in Herr. Of frost, it is recorded in Old English, perhaps expressing the resemblance of the white feathers of frost to an old man's beard. Used as an attribute of boundary stones in Anglo-Saxon, perhaps in reference to being gray with lichens, hence its appearance in place-names.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
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Definitions of hoary from WordNet
showing characteristics of age, especially having grey or white hair; "whose beard with age is hoar"-Coleridge;