- orphic
- orphrey
- orpiment
- orpin
- orpine
- orpington
- orra
- orrery
- orrhology
- orrhomeningitis
- orris
- orris-root
- orsellic
- ort
- orthal
- orthaxial
- orthesis
- orthicon
- orthistyle
- orthmorphism
- ortho position
- orthoamitosis
- orthobiosis
- orthoblastic
- orthoboric acid
- orthocarbonic acid
- orthocenal circles
- orthocenter
- orthocentre
- orthocentric
- orthocephalic
- orthocephalous
- orthocephaly
- orthochromatic
- orthochromatic emulsion
- orthoclase
- orthocomplement
- orthocytosis
- orthodeuterium
- orthodigita
- orthodontia
- orthodontic
- orthodontic appliance
- orthodontics
- orthodontist
- orthodox
- orthodoxy
- orthodromic
- orthodromic track
- orthoenteric
- orthoepic
- orthoepist
- orthoepy
- orthoevolution
- orthoferrites
- orthoformic acid
- orthogamous
- orthogamy
- orthogeneiss
- orthogenesis
- orthogenetic
- orthogenic
- orthognal transformation
- orthognathia
- orthognathic
- orthognathism
- orthognathous
- orthogonal
- orthogonal antennas
- orthogonal basic
- orthogonal circles
- orthogonal clearance
- orthogonal complement
- orthogonal cone
- orthogonal coordinates
- orthogonal cut
- orthogonal cutting
- orthogonal expansion
- orthogonal functions
- orthogonal group
- orthogonal involution
- orthogonal matrix
- orthogonal plane
- orthogonal polarization
- orthogonal polynomials
- orthogonal process
- orthogonal projection
- orthogonal scanning
- orthogonal sequences
- orthogonal sets
- orthogonal signals
- orthogonal substitution
- orthogonal surface
- orthogonal system
- orthogonal tests
- orthogonal trajectory
- orthogonal transformation
- orthogonal transmission
- orthogonality
- orthogonalization