1. Someone who keeps, upholds, or supports something: Henry was a conscientious objector and didn’t join the army because he was a strict maintainer of pacifism.
2. A person who tends to maintenance work: The janitor of the school was a maintainer along with the cleaning team and they all kept the school clean and did any repair work that was necessary.
3. A device which keeps the teeth in a proper position: After Linda spent about three years wearing braces, she then had to wear a maintainer to keep the right arrangement of her teeth in place.