Why is a Brazil nut not a true botanical nut?

The Brazil nut is not a true botanical nut because it is technically a seed derived from a capsule fruit, rather than a dry, hard fruit that does not split open at maturity.1

In botany, a true nut is defined as a dry, hard fruit that develops from more than one carpel and does not open to release its single seed. Examples of true nuts include the chestnut, hazelnut, and acorn.1

In contrast, the Brazil nut grows inside a large, spherical, hard-walled fruit pod that contains multiple seeds arranged like the sections of an orange. While these seeds are commonly referred to as "nuts" in a culinary context due to their high fat content and hard shells, they do not meet the strict botanical criteria for a nut.213