grizzly vs grey-headed

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

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

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

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

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

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

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