primeval (adj) – belonging to the first or earliest ages of recorded time; original; primitive (also primaeval)
BREAKDOWN: PRIM- (first) + EV- (age) + -AL (pertaining to)
This word is built on the root PRIM-, which means first, chief, or foremost.
Common PRIM- words include primary, primarily, primate, prime, and primitive.
More esoteric PRIM- words include primatology, primigenial, and primiparous.