atavist vs organism

atavist and organism both are nouns.

Word	Noun	Adjective	Verb	Adverb
atavist	Yes	No	No	No
organism	Yes	No	No	No

As nouns, organism is a hypernym of atavist; that is, organism is a word with a broader meaning than atavist:

atavist: an organism that has the characteristics of a more primitive type of that organism
organism: a living thing that has (or can develop) the ability to act or function independently

Other hypernyms of atavist include being.

atavist (noun)	organism (noun)
an organism that has the characteristics of a more primitive type of that organism	a living thing that has (or can develop) the ability to act or function independently
	a system considered analogous in structure or function to a living body