To fatten means to make something fatter or heavier by feeding it more food. Farmers fatten cattle, pigs, or turkeys before taking them to market by giving them extra grain and nutrients. The animals grow larger and heavier, which is the farmer's goal.

The word can also describe what happens when you eat too much yourself. If someone says a big Thanksgiving dinner will fatten them up, they mean all that food will make them gain weight. Parents might try to fatten up a child who's been sick and lost weight by making sure they eat nutritious meals.

You'll also hear fatten used about money and profits. A company might try to fatten its profits by cutting costs or selling more products. A person might fatten their wallet or bank account by saving money carefully. In this sense, fatten means to make bigger or more substantial, even though no actual eating is involved. The phrase fatten the pig suggests preparing for something bigger ahead, whether that's a sale, a celebration, or just building up strength and resources.