Peanuts grow underground.
True nuts, like walnuts and almonds grow on trees.
Rather than being nuts, peanuts fall into the legume category. Like beans and peas, peanuts are edible seeds enclosed in pods. Legumes, including peanuts, provide the best source of concentrated proteins in the plant kingdom.
The physical structure and nutritional benefits of peanuts closely resemble those of other legumes. However peanuts in diets and cuisines do closely resemble those of nuts.
Peanuts develop underground as part of the root system of the peanut plant, while real nuts normally grow inside of a fruit.
Real nuts are therefore part of the reproductive system of a plant, while peanuts are part of the nutrient system of the plant.
To be honest, must people have never thought of the peanut being anything other than a peanut.
However, information like this is good to know just like it is good to know that a tomato is a fruit and not a vegetable. Also, graham crackers and animal crackers are really cookies.