It's a descriptive term, often used for:
* Large lakes or rivers: Wainui is a common place name for such bodies of water.
* The ocean: It can refer to the vast expanse of the sea, especially when it's rough or stormy.
* A person with a large amount of knowledge or wisdom: Figuratively, it can describe someone who has a deep understanding of a subject.
The word is formed from two parts:
* Wai: Water
* Nui: Big, large
So, "Wainui" literally translates to "big water".