Is Cacao, from which chocolate is made, a nut or a fruit?

A seed, contained in a pod
https://en.wikipedia.org/wiki/Cacao

The cacao bean is actually the SEED of the fruit often thought of as a culinary nut.

Chocolate is made from the seeds of a plant called Theobroma cacao. The seeds are dried and roasted and then processed to form cocoa, the basic ingredient in chocolate and chocolate products.

By 1828, the cocoa press was developed. The press enabled workers to extract cocoa butter from the cacao bean. Ground roasted beans and sugar were added to the cocoa butter to produce dark "eating" (solid) chocolate. The first commercially prepared dark chocolate was produced in about 1847. Milk chocolate, made with the addition of dried milk solids, was developed by the Swiss in about 1876.

http://www.rawcacao.com/