flagellum vs outgrowth

flagellum and outgrowth both are nouns.

Word	Noun	Adjective	Verb	Adverb
flagellum	Yes	No	No	No
outgrowth	Yes	No	No	No

As nouns, outgrowth is a hypernym of flagellum; that is, outgrowth is a word with a broader meaning than flagellum:

flagellum: a lash-like appendage used for locomotion (e.g., in sperm cells and some bacteria and protozoa)
outgrowth: a natural prolongation or projection from a part of an organism either animal or plant

Other hypernyms of flagellum include appendage, process.

flagellum (noun)	outgrowth (noun)
a lash-like appendage used for locomotion (e.g., in sperm cells and some bacteria and protozoa)	a natural prolongation or projection from a part of an organism either animal or plant
a whip used to inflict punishment	the gradual beginning or coming forth
	a natural consequence of development