The coconut is surprisingly complicated, a seed and more.

Botanically speaking, a coconut is a fibrous one-seeded drupe, also known as a dry drupe. However, when using loose definitions, the coconut can be all three: a fruit, a nut, and a seed.

Full article is worth reading:

https://www.loc.gov/everyday-mysteries/item/is-a-coconut-a-f....