grizzly vs gray-headed

grizzly is a noun but gray-headed is not a noun.

Word	Noun	Adjective	Verb	Adverb
grizzly	Yes	Yes	No	No
gray-headed	No	Yes	No	No

As adjectives, grizzly and gray-headed are synonyms defined as:

grizzly and gray-headed: showing characteristics of age, especially having grey or white hair

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

grizzly (noun)	gray-headed (noun)
powerful brownish-yellow bear of the uplands of western North America

grizzly (adjective)	gray-headed (adjective)
showing characteristics of age, especially having grey or white hair	showing characteristics of age, especially having grey or white hair