fertilized egg vs fauna

fertilized egg and fauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
fertilized egg	Yes	No	No	No
fauna	Yes	No	No	No

As nouns, fauna is a hypernym of fertilized egg; that is, fauna is a word with a broader meaning than fertilized egg:

fertilized egg: an animal organism in the early stages of growth and differentiation that in higher forms merge into fetal stages but in lower forms terminate in commencement of larval life
fauna: a living organism characterized by voluntary movement

Other hypernyms of fertilized egg include animal, animate being, beast, brute, creature.

fertilized egg (noun)	fauna (noun)
an animal organism in the early stages of growth and differentiation that in higher forms merge into fetal stages but in lower forms terminate in commencement of larval life	a living organism characterized by voluntary movement
	all the animal life in a particular region or period