The Collaborative International Dictionary of English v.0.48:

Hoar \Hoar\, v. t. [AS. h[=a]rian to grow gray.]
   To become moldy or musty. [Obs.] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hoar \Hoar\, a. [OE. hor, har, AS. h[=a]r; akin to Icel.
   h[=a]rr, and to OHG. h[=e]r illustrious, magnificent; cf.
   Icel. Hei[eth] brightness of the sky, Goth. hais torch, Skr.
   k[=e]tus light, torch. Cf. Hoary.]
   1. White, or grayish white; as, hoar frost; hoar cliffs.
      "Hoar waters." --Spenser.
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   2. Gray or white with age; hoary.
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            Whose beard with age is hoar.         --Coleridge.
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            Old trees with trunks all hoar.       --Byron.
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   3. Musty; moldy; stale. [Obs.] --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hoar \Hoar\, n.
   Hoariness; antiquity. [R.]
   [1913 Webster]

         Covered with the awful hoar of innumerable ages.
                                                  --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hoar
    adj 1: showing characteristics of age, especially having grey or
           white hair; "whose beard with age is hoar"-Coleridge;
           "nodded his hoary head" [syn: grey, gray, grey-
           haired, gray-haired, grey-headed, gray-headed,
           grizzly, hoar, hoary, white-haired]
    n 1: ice crystals forming a white deposit (especially on objects
         outside) [syn: frost, hoar, hoarfrost, rime]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "hoar":
   Jack Frost, advanced, advanced in life, advanced in years, aged,
   along in years, ancient, argent, argentine, black frost, canescent,
   chalky, cretaceous, elderly, fleecy-white, frost, frost line,
   frost smoke, frosted, frosty, gray, gray with age, gray-haired,
   gray-headed, grizzled, grizzly, grown old, hoarfrost, hoary,
   killing frost, lactescent, lily-white, marble, marmoreal, milky,
   niveous, old, old as Methuselah, patriarchal, platinum, pure white,
   rime, rime frost, senectuous, sharp frost, silver, silvered,
   silvery, snow-white, snowy, swan-white, venerable, white,
   white as snow, white frost, white with age, white-bearded,
   white-crowned, white-haired, wrinkled, wrinkly, years old