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