Nouns starting with the letter O are listed here. Many types of nouns are shown which can be helpful for writing engaging text.

oak, oath, oathe, oatmeal.

obedience, obelisk, obesity, object, objectification, objection, objective, objectivity, objector, obligation, oblige, obliteration, oblivion, oboist, obscenity, obscurity, observance, observation, observer, obsession, obsidian, obstacle, obstructionist, obverse.

ocarina, occasion, occlusion, occupancy, occupant, occupation, occurrence, ocean, oceanography, ocelot, ocher, ochre, octahedron, octoroon.

odor, odyssey.

oep.

offal, offender, offense, offer, offering, offersey, office, officer, official, officialdom, offing, offspring.

oil, oilcloth, oilheating, oilseed, ointment, oiticica.

oleomargarine, olive.

ome, omelet, omen, omission, ommission, omnipotence.

oneupmanship, onion, onlooker, onrush, onset, onslaught.

ooh, ooze.

open, opener, opening, opera, operand, operation, operator, operetta, opinion, opium, opponent, opportunism, opportunity, opposite, opposition, oppression, opprobrium, optimality, optimism, optimization, optimum, option.

oracle, oration, orator, oratorio, oratory, orb, orbit, orchard, orchestra, orchestration, ordeal, order, ordering, orderly, ordinance, ordinary, ordnance, organ, organdy, organification, organism, organist, organization, orgasm, orgone, orgy, orientation, origin, original, originality, origination, ornament, ornamentation, orphan, orphanage, orthicon, orthodontist, orthography, orthophosphate.

oscillation, oscillator, osmium, ossification, ostracism.

otter.

ounce, ouster, outback, outbreak, outburst, outcast, outcome, outcry, outfield, outfielder, outfit, outflow, outgrowth, outhouse, outing, outlaw, outlawry, outlay, outlet, outline, outlook, outpatient, outpost, outpouring, output, outrage, outreach, outset, outside, outsider.

oval, ovation, oven, overall, overcast, overcoat, overcrowding, overestimation, overexploitation, overflow, overhang, overhaul, overhauling, overhead, overheating, overlay, overload, overnight, overpayment, overpopulation, overpressure, overprotection, overriding, overrun, overseer, oversight, oversimplification, overthrow, overtime, overture, overweight.

owi, owl, owner, ownership, owning.

oxalate, oxcart, oxen, oxidation, oxide, oxygen, oxytetracycline.

oyster.

ozone.

There are many other posts on Noun1.com to view that are like the above O nouns list but which start with different letters. Of all the parts of speech used in constructing a sentence, the noun is one of the most important, and these examples of nouns beginning with O can hopefully help one find the perfect word.