Hoary, a.
1. White or whitish."The hoary willows." Addison.
2. White or gray with age; hoar; as, hoary hairs. Reverence the hoary head. Dr. T. Dwight.
3. Hence, remote in time past; as, hoary antiquity.
4. Moldy; mossy; musty. [Obs.] Knolles.
4 more senses
5. (Zoöl.)
Of a pale silvery gray.
6. (Bot.)
Covered with short, dense, grayish white hairs; canescent. Hoary bat (Zoöl.), an American bat (Atalapha cinerea), having the hair yellowish, or brown, tipped with white.
Shades of meaning
Fernald has no entry of its own for hoary; he lists it under old.
Where he writes about it:
Gray, hoary, and moldering refer to outward and visible tokens of age. — from old
Decrepit, gray, and hoary refer to the effects of age on the body exclusively; senile upon the mind also; as, a decrepit frame, senile garrulousness. — from old