Are you nuts? Peanut is not a nut?
To answer this, let us define nut. According to the dictionary, a nut is a small dry fruit with a hard shell. Examples of this are chestnuts, hazelnuts and acorns.
Peanuts are also called nuts but are not botanically nuts (refer back to the definition). Along with peas, beans and lentils, they are categorized as legumes. Legume is defined as a type of plant with seeds that grow in pods.
Cashews, together with almonds, pecans and walnuts, are seeds of a drupe fruit. A drupe is a fleshy fruit with hard inner layer surrounding the seed. Examples of drupes are mango, apricot, cherry, etc.
Extra: Edible nuts are most healthy in their raw form.