macrocephalic vs macrocephaly

macrocephalic is not a noun while macrocephaly is a noun.

Word	Noun	Adjective	Verb	Adverb
macrocephalic	No	Yes	No	No
macrocephaly	Yes	No	No	No

macrocephalic (noun)	macrocephaly (noun)
	an abnormally large head; differs from hydrocephalus because there is no increased intracranial pressure and the overgrowth is symmetrical

macrocephalic (adjective)	macrocephaly (adjective)
having an exceptionally large head and brain