A nutrient is not the whole meal. It is a useful piece inside food — or inside soil, for a plant — that a living body must have so it can stay alive and grow. Protein, fat, carbohydrate, vitamins, minerals, water: these are the big names. A banana is food; the potassium and the sugar in it are nutrients. Plants pull nutrients from the ground; animals get them by eating. People also talk about empty food, meaning it fills you up but gives you few nutrients. The word is at home in science class and on the back of a cereal box. It is a little more technical than “something good in food,” but it is not rare or fancy. Though actually, nutrition is the whole topic or the feeding process; a nutrient is one building-block inside that story. The word comes from a Latin verb that meant to suckle or to feed a child, so at root it is about feeding, not about chemistry. We later stretched it to plants and to pills.