- Orthochromasia Noun
- Orthoclase Noun
- Orthocomplement Noun
- Orthocomplementation Noun
- Orthocoupler Noun
- Orthodentin Noun
- Orthodiagram Noun
- Orthodiagraph Noun
- Orthodiagraphy Noun
- Orthodontia Noun
- Orthodontics Noun
- Orthodontist Noun
- Orthodontology Noun
- Orthodoxy Noun
- Orthodrome Noun
- Orthoepist Noun
- Orthoepy Noun
- Orthoferrite Noun
- Orthogenesis Noun
- Orthogeosyncline Noun
- Orthognathia Noun
- Orthognathism Noun
- Orthognathy Noun
- Orthogonality Noun
- Orthogonalization Noun
- Orthograde Adj Noun
- Orthography Noun
- Orthohydrogen Noun
- Orthokeratinization Noun
- Orthokeratology Noun
- Orthokeratosis Noun
- Ortholattice Noun
- Orthology Noun
- Orthometer Noun
- Orthomyxovirus Noun
- Orthonormality Noun
- Orthonormalization Noun
- Orthopaedics Noun
- Orthopaedist Noun
- Orthopantomogram Noun
- Orthopantomograph Noun
- Orthopantomography Noun
- Orthopedics Noun
- Orthopedist Noun
- Orthophony Noun
- Orthophoria Noun
- Orthophotograph Noun
- Orthophotomap Noun
- Orthophyre Noun
- Orthopnea Noun
- Orthopnoea Noun
- Orthopole Noun
- Orthopositronium Noun
- Orthopoxvirus Noun
- Orthopraxia Noun
- Orthopraxy Noun
- Orthoprojector Noun
- Orthopsychiatrist Noun
- Orthopsychiatry Noun
- Orthopter Noun