full-grown vs fully grown

full-grown and fully grown both are adjectives.

Word	Noun	Adjective	Verb	Adverb
full-grown	No	Yes	No	No
fully grown	No	Yes	No	No

As adjectives, full-grown and fully grown are synonyms defined as:

Other synonyms of full-grown include adult, big, grown, grownup.

full-grown (adjective)	fully grown (adjective)
(of animals) fully developed	(of animals) fully developed