Note: in BRIT, also use 'primaeval'
1.
You use primeval to describe things that belong to a very early period in the history of the world. (FORMAL)
...the dense primeval forests that once covered inland Brittany.
= primordial
ADJ: usu ADJ n
2.
You use primeval to describe feelings and emotions that are basic and not the result of thought.
...a primeval urge to hit out at that which causes him pain.
ADJ: usu ADJ n