Nouns That Start With O (English Vocabulary)

In this article, I am going to provide you a comprehensive list of Nouns That Start With O. First, need to know what is a noun? Nouns are one of the nine parts of speech. To understand the meaning of a noun, one of the easiest explanations is that it is a word used for the person, object, place, idea, event, quality, quantity, and substance. Nouns are the most common words used in English. I have enlisted an extensive collection of nouns that start with O.

We have over 1000 cool words that will assist you about words that start with O.

Nouns that start with O list in English is arranged in alphabetical order, which helps students understand the O nouns in the right way.

Read also: “Adjectives That Start With O?”

It is a fact that there are too many lovely nouns that start with O in English; it is challenging to choose to include them in the index.

READ: Positive Words That Start With O

Nouns That Start With O List

Here are fundamental nouns that start with O in English that will enhance your English Vocabulary. You will get here 3 Letter nouns, 4 letter nouns, 5 letter nouns, 6 letter nouns, 7 letter nouns and 8 letter nouns!

Oak	Okay	Orbiter	Outrageousness
Oasis	Oke	Orbitosphenoid	Outrance
Oath	Okey	Orbivirus	Outreach
Oathe	Okimono	Orc	Out-Relief
Oatmeal	Okra	Orca	Outremer
Ob	Okrug	Orcein	Outrider
Oba	Ola	Orchard	Outrigger
Obbligato	Old	Orcharding	Outro
Obduction	Oldie	Orchestra	Outseam
Obduracy	Oldman	Orchestra-Pit	Outset
Obdurateness	Oldness	Orchestration	Outside
Obe	Old-School	Orchestrator	Outsider
Obeah	Oldster	Orchestre	Outsiderhood
Obeche	Oldstyle	Orchestrion	Outskirt
Obedience	Old-Timer	Orchid	Outsole
Obediency	Oleander	Orchidectomy	Outspan
Obeisance	Oleate	Orchis	Outspokenness
Obelisk	Olecranon	Ord	Outstation
Obesity	Oleo	Orde	Outswinger
Obex	Oleograph	Ordeal	Out-Swinger
Obeyance	Oleomargarine Olive	Order	Out-Thereness
Obfuscation	Oleoyl	Ordering	Out-Tray
Obi	Olestra	Orderliness	Outturn
Obit	Oleum	Orderly	Out-Turn
Obiter	Oleyl	Ordinance	Outwash
Obituarist	Olf	Ordinand	Outwork
Obituary	Olfaction	Ordinariness	Outworker
Object	Olfactometer	Ordinary	Outworld
Objectification	Olfactory	Ordinate	Ouvert
Objection	Oligarch	Ordination	Ouvrier
Objective	Oligarchy	Ordnance	Ouvriere
Objectiveness	Oligo	Ordo	Ouzel
Objectivism	Oligodendrocyte	Ordre	Ouzo
Objectivist	Oligomenorrhoea	Ordure	Oval
Objectivity	Oligomer	Ore	Ovalbumin
Objector	Oligonucleotide	Orebody	Ovangkol
Oblast	Oligopoly	Orefield	Ovariotomy
Oblate	Oligosaccharide	Oregano	Ovary
Oblation	Oligospermia	Orenda	Ovation
Obligation	Oligotrophication	Orf	Oven
Obligato	Oliguria	Orfe	Ovenware
Obligatoriness	Oliphant	Org	Over
Oblige	Oliphaunt	Organ	Overabundance
Obligee	Oliva	Organdie	Overaccumulation
Obligor	Olive	Organdy	Overactivity
Oblique	Oliver	Organelle	Overall
Obliqueness	Olivet	Organicism	Overanxiety
Obliquity	Olivewood	Organicist	Overarm
Obliquus	Olivine	Organification	Overbalance
Obliteration	Olla	Organisation	Overbar
Oblivion	Ollie	Organiser	Overbite
Obliviousness	Ology	Organism	Overbridge
Oblong	Oloroso	Organist	Overcapacity
Obloquy	Olsalazine	Organization	Overcast
Obnoxiousness	Olympiad	Organizer	Overcharge
Oboe	Om	Organogenesis	Overclothing
Oboist	Ombre	Organology	Overcoat
Obol	Ombudsman	Organon	Overcollection
Obs	Ombudsperson	Organophosphate	Overcommitment
Obscenity	Ome	Organum	Overcompensation
Obscurantism	Omega	Organza	Overconcentration
Obscurantist	Omelet	Orgasm	Overconcern
Obscuration	Omelette	Orgel	Overconfidence
Obscurity	Omen	Orgone	Overconsumption
Obsequies	Omentum	Orgy	Over-Consumption
Obsequiousness	Omeprazole	Oribi	Overcorrection
Observability	Omer	Orichalcum	Overcrowding
Observance	Omerta	Oriel	Overdependence
Observation	Omi	Orient	Overdetermination
Observator	Omicron	Orientalism	Overdevelopment
Observatory	Omission	Orientalist	Overdispersion
Observer	Ommatidium	Orientation	Overdoor
Obsession	Ommission	Orienteering	Overdosage
Obsessiveness	Omnibus	Orifice	Overdose
Obsidian	Omnicompetence	Oriflamme	Overdraft
Obsolescence	Omnipotence	Origami	Overdraught
Obsoleteness	Omnipotent	Origanum	Overdrive
Obstacle	Omnipresence	Origin	Overdub
Obstetrician	Omniscience	Original	Overearnestness
Obstinacy	Omnium	Originality	Overeater
Obstruction	Omnivore	Origination	Overemphasis
Obstructionism	Omphalos	Originator	Overestimate
Obstructionist	Omul	Origo	Overestimation
Obstructiveness	On	Oriole	Over-Excitement
Obstructor	Onanism	Orl	Overexertion
Obtrusiveness	Once-Over	Ormolu	Overexpansion
Obtuseness	Onchocerciasis	Ornament	Overexploitation
Obverse	Oncogene	Ornamentalism	Overexposure
Obviousness	Oncogenesis	Ornamentation	Overexpression
Oby	Oncologist	Ornamenter	Overfamiliarity
Oca	Oncology	Ornateness	Overfishing
Ocarina	Oncomouse	Ornithischian	Overflight
Occasion	Oncoprotein	Ornithologist	Overflow
Occident	Oncost	Ornithology	Overfunding
Occidental	Oncostatin	Ornithopter	Overgarment
Occiput	Oncovin	Orogen	Overgeneralization
Occlusion	Ondansetron	Orogenesis	Overglaze
Occult	One-Dayer	Orogeny	Overgo
Occultation	Oneiromancy	Oropharynx	Overgrazing
Occultism	One-Itis	Orosomucoid	Overgrowth
Occultist	One-Liner	Orotundity	Overhand
Occupance	Oneness	Oroya	Overhang
Occupancy	One-Nighter	Orphan	Overhaul
Occupant	One-Of-A-Kind	Orphanage	Overhauling
Occupation	One-Off	Orpharion	Overhead
Occupier	One-Piece	Orpin	Overhearer
Occurence	Oner	Orrery	Overheating
Occurrence	Onerousness	Orris	Overinclusion
Ocean	One-Shot	Ort	Overindebtedness
Oceanarium	One-Sidedness	Orthicon	Overindulgence
Oceanfront	Oneupmanship	Ortho	Overinvestment
Oceanographer	One-Upmanship	Orthodontics	Overinvolvement
Oceanography	One-Year-Old	Orthodontist	Overkill
Ocellus	Oni	Orthodoxy	Overlap
Ocelot	Onion	Orthogenesis	Overlay
Oche	Onlap	Orthogneiss	Overlayer
Ocher	Onlay	Orthogonality	Overlength
Ochre	Onlooker	Orthography	Overload
Ocker	Only	Orthomorphism	Overlock
Oct	Onomastics	Orthopaedics	Overlooker
Octadecyl	Onomatopeia	Orthopaedist	Overlord
Octaeteris	Onomatopoeia	Orthopedics	Overlordship
Octagon	Onrush	Orthophosphate	Overman
Octahedron	Onset	Orthoptera	Overmantel
Octal	Onslaught	Orthopyroxene	Overnight
Octamer	Ontogenesis	Orvieto	Overpass
Octane	Ontogeny	Oryx	Overpayment
Octapeptide	Ontology	Orzo	Overplus
Octave	Onus	Os	Overpopulation
Octavius	Onyx	Oscar	Overprescription
Octavo	Oocyte	Oscillation	Overpressure
Octet	Oodles	Oscillator	Overprint
Octofoil	Oogenesis	Oscillograph	Overproduction
Octogenarian	Ooh	Oscilloscope	Overprotection
Octopole	Oolite	Osculation	Overprotectiveness
Octopus	Oolong	Osh	Overprovision
Octopush	Oompah	Osha	Overreach
Octopussy	Oomph	Osier	Overreaction
Octoroon	Ooze	Osmium	Overreliance
Octreotide	Op	Osmolality	Overrepresentation
Octyl	Op.	Osmolarity	Override
Oculist	Opacification	Osmometer	Overriding
Oculus	Opacity	Osmometry	Overruler
Od	Opah	Osmoregulation	Overrun
Oda	Opal	Osmose	Overseer
Odalisque	Opalescence	Osmosis	Oversensitiveness
Oddball	Opaline	Osmotherapy	Oversensitivity
Odd-Bod	Opaqueness	Osmunda	Overshirt
Oddity	Opcode	Osprey	Overshoot
Oddness	Open	Ossia	Oversight
Ode	Opener	Ossification	Oversimplification
Oden	Open-Handedness	Ossuary	Overskirt
Odeon	Open-Heartedness	Ost	Oversman
Odium	Opening	Osteitis	Overspecialization
Odometer	Openmindedness	Ostension	Overspender
Odonatist	Open-Mindedness	Ostentation	Overspill
Odontoid	Openness	Osteoarcheologist	Overspray
Odontologist	Openside	Osteoarthritis	Overstability
Odor	Open-Side	Osteogenesis	Overstatement
Odorant	Openwork	Osteology	Oversteer
Odour	Open-Work	Osteolysis	Overstimulation
Odyssey	Oper	Osteoma	Overstrike
Oe	Opera	Osteomalacia	Oversubscription
Oecology	Operability	Osteomyelitis	Oversupply
Oedema	Operand	Osteonecrosis	Overtaxation
Oenology	Operant	Osteopath	Overthrow
Oep	Operatics	Osteopathy	Overthrowal
Oesophagectomy	Operating-System	Osteopenia	Overthrust
Oesophagitis	Operation	Osteoporosis	Overtime
Oesophagogastroduodenoscopy	Operationalisation	Osteosarcoma	Overtone
Oesophagogram	Operationalism	Osteospermum	Overtrading
Oesophagoscopy	Operationalization	Ostinato	Overtreatment
Oesophagus	Operative	Ostiole	Overtrick
Oestradiol	Operator	Ostler	Overtrousers
Oestriol	Operatorship	Ostmark	Overture
Oestrogen	Operculum	Ostracism	Overtype
Oestrus	Operetta	Ostracization	Overuse
Oeuvre	Operon	Ostranenie	Overvaluation
Off	Ophiolite	Ostrich	Overview
Offal	Ophthalmia	Otaku	Overvoltage
Offchance	Ophthalmologist	Otalgia	Overwatch
Off-Chance	Ophthalmology	Oth	Overwear
Offcut	Ophthalmoscope	Other	Overweening
Offence	Ophthalmoscopy	Otherness	Overweight
Offender	Opiate	Otherworld	Overwhelm
Offense	Opine	Otherworldliness	Overwork
Offensive	Opinion	Otitis	Overworld
Offensiveness	Opioid	Otolaryngology	Overwrap
Offer	Opium	Otosclerosis	Oviduct
Offeree	Opossum	Otoscopy	Ovine
Offerer	Oppertunity	Ottar	Oviposition
Offering	Oppidum	Otter	Ovipositor
Offeror	Oppo	Otterskin	Ovoid
Offersey	Opponent	Otto	Ovolo
Offertory	Opportunism	Ottoman	Ovulation
Offhandedness	Opportunist	Ouabain	Ovule
Office	Opportunity	Oubliette	Ovulum
Officer	Opposability	Oughtness	Ovum
Officership	Opposite	Ouguiya	Ower
Official	Oppositeness	Ouija	Owings
Officialdom	Opposition	Oul	Owl
Officialese	Oppositionist	Ounce	Owlet
Officialism	Oppression	Ouster	Owling
Officiant	Oppressiveness	Out	Owner
Officiousness	Oppressor	Outa	Owner-Operator
Offie	Opprobrium	Outage	Ownership
Offing	Oppy	Outback	Owning
Off-Licence	Oprichnina	Outboard	Owre
Off-License	Opry	Outbound	Ox
Offload	Opsimath	Outbreak	Oxalate
Offramp	Opsin	Outbreeding	Oxalis
Off-Roader	Opsonisation	Outbuilding	Oxblood
Off-Season	Optic	Outburst	Oxbow
Offset	Opticals	Outcast	Oxcart
Offshoot	Optician	Outcaste	Oxen
Offside	Opticks	Outcome	Oxer
Offspinner	Optimality	Outcrop	Oxeye
Offspring	Optimisation	Outcry	Oxfendazole
Offtake	Optimiser	Outdatedness	Oxford
Off-White	Optimism	Outdoorsman	Oxhide
Offworlder	Optimist	Outer	Oxicam
Off-Worlder	Optimization	Outercoat	Oxidant
Oflag	Optimum	Outer-Space	Oxidase
Og	Option	Outerwear	Oxidation
Ogam	Optionality	Outfall	Oxide
Ogee	Optocoupler	Outfield	Oxidisation
Oggy	Optoelectronics	Outfielder	Oxidoreductase
Ogi	Optometrist	Outfielding	Oxime
Ogle	Optometry	Outfit	Oximeter
Ogonek	Opt-Out	Outfitter	Oximetry
Ogre	Optronics	Outflow	Oxo
Ogress	Opulence	Outgate	Oxocarbon
Ohana	Opuntia	Outgroup	Oxon
Ohio	Opus	Outgrowth	Oxtail
Ohm	Orache	Outhaul	Oxy
Oidium	Oracle	Outhouse	Oxyacetylene
Oik	Oracy	Outing	Oxyanion
Oikos	Oral	Outland	Oxybutynin
Oil	Oralism	Outlandishness	Oxyfluoride
Oilbird	Oralist	Outlands	Oxygen
Oilcan	Orality	Outlaw	Oxygenase
Oilcloth	Oranda	Outlawry	Oxygenation
Oiler	Orang	Outlay	Oxygenator
Oilfield	Orange	Outlet	Oxyhaemoglobin
Oilheating	Orangeade	Outline	Oxymoron
Oiliness	Orangerie	Outliner	Oxyrhynchus
Oilman	Orangery	Outlook	Oxytetracycline
Oilrig	Orang-Outang	Outmigration	Oxytocin
Oilseed	Orangutan	Out-Of-Doors	Oyer
Oilskin	Orang-Utan	Out-Of-Towner	Oyl
Oilstone	Orangutang	Outpatient	Oyster
Oilwell	Oration	Out-Patient	Oystercatcher
Oink	Orator	Outperformance	Oz
Ointment	Oratorio	Outplacement	Ozokerite
Oiticica	Oratory	Outport	Ozonation
Ojha	Orb	Outpost	Ozone
Oka	Orbit	Outpouring	Ozonesonde
Okada	Orbita	Output	Ozoniser
Okapi	Orbital	Outrage

This nouns that start with O List presents you with every noun useful to enhance your English vocabulary.

Conclusion

I hope you have enjoyed our list about nouns that start with O. According to my opinion read the above easy listing of O nouns to expand your English learning skills.

Guide your children to master these basic but commonly used nouns that start with O by following the example provided above. Keep this list of English vocabulary to be handy for use in the future.

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Recap of what we just learned?

• What is a noun?
• Nouns That Start With O
• Nouns That Start With O List in English

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