* Therapy: The treatment of illness or injury.
* Therapist: A person who practices therapy.
* Therapeutic: Having a healing or curative effect.
* Therapuetic: (Less common spelling) Having a healing or curative effect.
* Thermotherapy: Treatment using heat or cold.
* Electrotherapy: Treatment using electricity.
* Phototherapy: Treatment using light.
* Chemotherapy: Treatment using chemicals.
There are also some less common words with this root, like therapeutist and therapeusis.