Not all nuts are nuts! The peanut especially is not even close to being a nut. It is actually in the legume family so closely related to soy beans and lentils.
Since I have a background in botany and ecology, I can also get a bit carried away with the actual botanical definition of a nut. In culinary terms a 'nut' is simply a dry seed borne from a tree. In botanical terms it is more complicated involving some delightful words like involucre and syncarpous gynoecium ...!!
So, if you want to sound infuriatingly pedantic and ridiculously knowledgeable, here is the definition of a true 'nut' (with translation from Botany-speak to English):
A nut is a fruit with a woody outer wall (pericarp). The fruit is developed from the female reproductive structure (gynoecium) where some parts of it are fused together (syncarpous). All true nuts do not open on their own when they mature (indehiscent). True nuts include the chestnut, acorn and hazelnut.
Some nuts that almost scrape into the true nut definition are dry drupes. (A term that sounds like a great insult...) Dry drupes are also indehiscent, but have an outer fleshy part that surrounds the seed. The outer parts dry up and the remaining husk is part of the ovary wall. Then there is a hard inner wall that surrounds the actual seed. Nuts in this category include almonds, pecans and macadamias.
Walnuts defy definition and are classed somewhat disparagingly as a pseudo-drupe (poor walnut).
However, we at Totally Nuts are very comfortable with our definition of nuts... the dry fruit of trees, that grows in a hard shell; can be activated; is full of nutrients and tastes delicious!