Say It: \ˌa-tə-ˈvis-tik\
Part of Speech: adjective
Definition (as defined by Merriam-Webster): relating to or characterized by reversion to something ancient or ancestral.
Used in a Sentence (aka How I Found It): “Some atavistic, survival-oriented part of her even remembered to choke up on the red maple rod, knowing it would maximize the force, and maximum force was good.” Just After Sunset by Stephen King
Origin: French, first used in 1833