This may sound nutty, but a peanut is technically not a nut.
Peanuts are legumes and are in the same family as peas and lentils. Unlike tree nuts, the peanut plant grows as a ground flower with its pods maturing underground. However, the protein in peanuts has a similar structure to those in tree nuts, such as almonds, Brazil nuts, cashews, hazelnuts, macadamia, pistachios, pecans, and walnuts. This is why people allergic to peanuts can also be allergic to tree nuts.