Peanuts, walnuts, almonds, cashews and pistachios aren’t nuts.

Peanuts, walnuts, almonds, cashews and pistachios aren’t nuts.

Nuts are defined as a simple, dry fruit with one seed (very occasionally two) in which the seed case wall becomes very hard at maturity. ... Peanuts, almonds, pistachios, cashews, horse chestnuts and pine nuts are not nuts. So the health warning on a packet of peanuts (“may contain nuts”) is, strictly speaking, untrue.

Almonds, for example, are in fact drupes, not nuts at all. Neither are cashews, pistachios and pine nuts. Many tree nuts are drupes, including walnuts and pecans (although confusingly these are known as drupaceous nuts as they difficult to categorise and are not true botanical nuts).

Thus, because of the plant's structural configuration, the edible portion of a cashew is botanically classified as a drupe seed. The seed and its outer shell are technically considered both the nut and the fruit, but the shell is inedible due to the presence of a toxic substance.

Tree nuts include almonds, Brazil nuts, cashews, hazelnuts, pecans, pistachios and walnuts. ... Nutmeg, water chestnut, butternut squash and shea nuts are not tree nuts (the term “nut” does not always indicate a tree nut) and are generally well tolerated by tree nut-allergic individuals.

Peanuts aren't actually a true nut; they're a legume (in the same family as peas and lentils). ... For this reason, people who are allergic to peanuts can also be allergic to tree nuts, such as almonds, Brazil nuts, walnuts, hazelnuts, macadamia nuts, pistachios, pecans, and cashews.