- orbitale
- orbital index
- orbital quantum number
- orbital sander
- orbital velocity
- orbiteer
- orbiter
- Orbiting Astronomical Observatory
- Orbiting Geophysical Observatory
- Orbiting Solar Observatory
- orb weaver
- orby
- orc
- orca
- Orcadian
- Orcagna
- orcein
- orch.
- orchard
- orchard bush
- orchard grass
- orchardist
- orchardman
- orchard oriole
- orchard valve
- orchectomy
- orchestra
- orchestral
- orchestrate
- orchestration
- orchestrina
- orchestrion
- orchi-
- orchid
- orchid-
- Orchidaceae
- orchidaceous
- orchidectomy
- orchid family
- orchido-
- orchidology
- orchidotomy
- orchid tree
- orchiectomy
- orchil
- orchis
- orchitis
- orchotomy
- orcinol
- OR circuit
- Orcus
- Orczy
- Ord
- ord.
- ordain
- ordained
- ordainee
- ordeal
- ordeal bean
- ordeal tree
- order
- order about
- order arms
- order bill of lading
- order-driven
- ordered
- ordered field
- ordered pair
- ordered set
- order in council
- ordering
- orderly
- orderly marketing agreement
- orderly officer
- orderly room
- Order of Australia
- order of battle
- order of business
- Order of Canada
- order of magnitude
- Order of Merit
- Order of Military Merit
- order of the day
- order of the day, the
- Order of the Garter
- Order of the Thistle
- order paper
- order port
- orders
- order someone about
- ordinal
- ordinal number
- ordinal numbers
- ordinal scale
- ordinance
- ordinand
- ordinariate
- ordinarily
- ordinary
- ordinary differential equation
- Ordinary grade
- ordinary income
- ordinary jubilee
- ordinary-language philosophy
- ordinary lay
- Ordinary level
- ordinary life insurance
- ordinary point
- ordinary rating
- ordinary ray
- ordinary seaman
- ordinary share
- ordinary shares
- ordinary stock
- ordinary wave
- ordinate
- ordination
- ordn.
- ordnance
- ordnance datum
- Ordnance Survey
- ordo
- Ordóñez
- ordonnance
- Ordos
- Ordovician
- ordure
- Ordzhonikidze
- ore
- öre
- Ore.
- oread
- orebody
- ore bridge
- Örebro
- orecchiette
- orectic
- ore dressing
- Oreg.
- oregano
- Oregon
- Oregon cedar
- Oregon City
- Oregon crab apple
- Oregon fir
- Oregon grape
- Oregonian
- Oregon myrtle
- Oregon pine
- Oregon trail
- Oregon Trail
- ore hearth
- oreide
- Orekhovo-Zuyevo
- Orel
- or else
- Orem
- Ore Mountains
- Orenburg
- orenda
- Orense
- Oreo
- oreodont
- Oreopithecus
- ore rotundo
- oreshoot
- Oresme
- Oresteia
- Orestes
- Orestes complex
- ore tanker
- orexis
- orf
- orfe
- Orfeo ed Euridice
- Orff
- orfray
- org
- org.
- organ
- organa
- organdie
- organdy
- organelle
- organelles
- organ grinder
- organ-grinder
- organic
- organic acid
- organically
- organic chemistry
- organic compounds
- organic disease
- organicism
- organic light-emitting diode
- organic molecule
- organic molecules
- organic psychosis
- organic solidarity
- organism
- organist
- organization
- organizational culture
- organizational psychology
- organization chart
- Organization for Economic Cooperation and Development
- Organization for European Economic Cooperation
- organization man
- Organization of African Unity
- Organization of American States
- Organization of Petroleum Exporting Countries
- organize
- organized
- organized labor
- organized militia
- organizer
- organ meat
- organo-
- organ of Corti
- organogenesis
- organogram
- organography
- organoleptic
- organology
- organomagnesium
- organometallic
- organon
- organophosphate
- organosilicon
- organosiloxane
- organotherapy
- organotin
- organotropism
- organ pipe
- organ-pipe cactus
- organ-pipe coral
- organ point
- organ screen
- organum
- organ whistle
- organza
- organzine
- orgasm
- orgasmic
- orgeat
- Orgetorix
- orgiastic
- orgone
- orgone box
- orgone energy
- orgulous
- orgy
- oribi
- orichalcum
- oriel
- oriel window
- orient
- Orient
- oriental
- Oriental
- Oriental alabaster
- Oriental almandine
- oriental beetle
- Oriental carpet
- Oriental cat's eye
- oriental cockroach
- Oriental emerald
- Oriental fruit moth
- Orientalia
- Orientalism
- Orientalist
- Orientalize
- Oriental poppy
- Oriental rug
- Oriental topaz
- orientate
- orientation
- Oriente
- orienteer
- orienteering
- Orient Express
- orifice
- orifice meter
- oriflamme
- orig.
- origami
- origan
- origanum
- Origen
- origin
- original
- original equipment manufacturer
- originalism
- originalist
- originality
- originally
- original sin
- originate
- origination fee
- originative
