Medical & Biological:
* Orthopedics: The branch of medicine dealing with the musculoskeletal system.
* Orthodontics: The branch of dentistry dealing with the alignment and straightening of teeth.
* Orthosis: A device used to support or correct a body part.
* Orthodox: Conforming to established standards or beliefs, especially in religion.
* Orthostatic: Relating to standing upright.
* Orthomolecular: Relating to the use of nutrients to treat disease.
Other:
* Orthography: The study of spelling and pronunciation.
* Orthographic: Relating to correct spelling or pronunciation.
* Orthogonal: Perpendicular or at right angles.
* Orthodox: Conforming to established standards or beliefs.
This list is not exhaustive, but it gives you a good starting point for understanding words with the "ortho-" root.