Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. Gray or white with age; hoary.

            Whose beard with age is hoar.         --Coleridge.

            Old trees with trunks all hoar.       --Byron.

   3. Musty; moldy; stale. [Obs.] --Shak.

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

         Covered with the awful hoar of innumerable ages.
                                                  --Burke.

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

Source : WordNet®

hoar
     n : ice crystals forming a white deposit (especially on objects
         outside) [syn: {frost}, {hoarfrost}, {rime}]

hoar
     adj : showing characteristics of age, especially having gray or
           white hair; "whose beard with age is hoar"-Coleridge;
           "nodded his hoary head" [syn: {gray}, {grey}, {gray-haired},
            {grey-haired}, {gray-headed}, {grey-headed}, {grizzly},
            {hoary}, {white-haired}]