bighead vs animal disease

bighead and animal disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
bighead	Yes	No	No	No
animal disease	Yes	No	No	No

As nouns, animal disease is a hypernym of bighead; that is, animal disease is a word with a broader meaning than bighead:

bighead: any of various diseases of animals characterized by edema of the head and neck
animal disease: a disease that typically does not affect human beings

bighead (noun)	animal disease (noun)
any of various diseases of animals characterized by edema of the head and neck	a disease that typically does not affect human beings