The Collaborative International Dictionary of English v.0.48:

Hoary \Hoar"y\, a.
   1. White or whitish. "The hoary willows." --Addison.
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   2. White or gray with age; hoar; as, hoary hairs.
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            Reverence the hoary head.             --Dr. T.
                                                  Dwight.
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   3. Hence, remote in time past; as, hoary antiquity.
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   4. Moldy; mossy; musty. [Obs.] --Knolles.
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   5. (Zool.) Of a pale silvery gray.
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   6. (Bot.) Covered with short, dense, grayish white hairs;
      canescent.
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   Hoary bat (Zool.), an American bat (Atalapha cinerea),
      having the hair yellowish, or brown, tipped with white.
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WordNet (r) 3.0 (2006):

hoary
    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]
    2: ancient; "hoary jokes" [syn: hoary, rusty]
    3: covered with fine whitish hairs or down [syn: canescent,
       hoary]