(Peanuts are actually a type of pea, so the health warning on a packet of peanuts (“may contain nuts”) is untrue. And people who are allergic to peanuts, are not necessarily allergic to nut nuts.
Pecans, sweet chestnuts, beech nuts, acorns and hazel nuts are nuts, but almonds, brazil nuts, pistachios, cashews, horse chestnuts and pine nuts are also not nuts.
Quite simply it's nuts!)
Source: QI on the BBC