Ortho
- Arene substitution patterns
- Chlordane
- List of commonly used taxonomic affixes
- Ortho Mode Transducer
- Ortho Pharmaceutical
- Ortho, Belgium
- Ortho-Clinical Diagnostics
- Ortho-DOT
- Ortho-cept
- Orthochromatic
- Orthodontics
- Orthodoxy
- Orthogonal
- Orthographic projection
- Orthomyxovirus
- Orthonormal
- Orthopedic
- Orthophotography
- Orthopraxy
- Orthoptera
- Orthos (disambiguation)
- Scotts Miracle-Gro Company