peanut
Synonym discussion
Sense: noun/1
For the food sense, peanut is the normal everyday word in general English. Groundnut is used in some regional varieties, especially in South Asian or African English, but it sounds less neutral in many international contexts. Nut is much broader and can mean almonds, walnuts, or many other hard edible seeds, so it is not exact enough when you specifically mean a peanut. Legume is the scientific group name that also includes beans and peas, and it is mainly used in biology or nutrition. In ordinary speech, say peanut butter, roasted peanuts, or a peanut allergy. At lunch, peanut butter sounds natural, while legume butter sounds wrong and groundnut butter sounds regional.
Etymology
Peanut is a compound created in English from pea and nut. The seed actually comes from a plant in the bean family, but speakers named it for its pea-like plant and its nut-like use as food. The word is transparent in modern English, so learners can still see the two older everyday words inside it.