✅ Reserve refers to something that is kept and stored either just in case or in preparation for a specific event or emergency, but it can also refer to intangible things (I kept a reserve of canned foods at the cabin; He had a reserve of energy). ✅ Reservoir refers to a large supply of something that can be drawn on or used when needed (The community had reservoirs of gas to be used for their buses). ✅ While you might be more familiar with the sense of reservoir meaning a large store of water, reservoir can also refer to a large store of intangible things like emotions (She possessed a reservoir of calm that others relied on). ✅ These two words have similar meanings, but reserve is used more widely for physical things.