fully grown vs full-grown

fully grown and full-grown both are adjectives.

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

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

Other synonyms of fully grown include adult, big, grown, grownup.

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