grey-haired vs hoar

grey-haired is not a noun while hoar is a noun.

Word	Noun	Adjective	Verb	Adverb
grey-haired	No	Yes	No	No
hoar	Yes	Yes	No	No

As adjectives, grey-haired and hoar are synonyms defined as:

grey-haired and hoar: showing characteristics of age, especially having grey or white hair

Other synonyms of grey-haired include gray-haired, gray-headed, gray, grey-headed, grey, grizzly, hoary, white-haired.

grey-haired (noun)	hoar (noun)
	ice crystals forming a white deposit (especially on objects outside)

grey-haired (adjective)	hoar (adjective)
showing characteristics of age, especially having grey or white hair	showing characteristics of age, especially having grey or white hair