Homonym: substitute (Replacement)
A "substitute" refers to something that takes the place of another item or person. For example, in cooking, a chef might use applesauce as a substitute for oil in a recipe to reduce fat content. Substitutes can also be found in various contexts, such as sports, where a substitute player replaces a teammate during a game.
In education, a substitute teacher fills in for a regular teacher who is absent. This ensures that students continue their learning without interruption. Substitutes are essential in many areas, providing alternatives that maintain functionality or performance when the original is unavailable.