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Nacreous: iridescent, pearly, like mother-of-pearl or nacre
Naiad: a nymph, a river, lake, fountain, or spring nymph or spirit
Naïveté: inexperience, quality of being naïve, artlessness
Nebulae: pl. collection of astral gases
Nemesis: source of harm or ruin, unconquerable foe or enemy, vengeful opponent
Nenuphar: a water lily, especially an Egyptian lotus
Neophyte: a novice, tyro, beginner

Nepenthe: drug of forgetfulness, anti-depression drug, remedy for sorrow
Nepheliad: cloud nymph, nymph designated or of the clouds
Nephew: the son of a brother or sister in relation to you
Nickelodeon: nickel theatre
Nimbus: dark, grey cloud bearing rain, splendid atmosphere or aura, cloudy radiance
Nimiety: excess, overabundance, superfluity
Nirvana: a place or state of rest, harmony, or pleasure
Niveous: snowy or resembling snow, like, of, relating to, or made of snow
Nocive: harmful, injurious
Noctilucence: cloud phenomenon typified by lights at night, visible or glowing at night
Nonchalant: feeling or appearing casually calm and relaxed, indifferent
Novae: pl. collapsing or dying star
Novella: short prose tale often characterised by moral teaching or satire
Novitiate: novice, the living place of a novice, the state of being a novice, neophyte
Nucleus: central part about which other parts are grouped or gathered
Nugacious: trifling, trivial, insignificant, unimportant, worthless
Nullibicity: state of non-existence, quality or state of being nowhere
Nullifidian: a person having no faith, religion, convictions, or beliefs
Numeral: symbol used to represent, denote, or symbolize a number
Numina: pl. presiding divinity or spirit of a place, creative energy, genius
Numismatics: study or collection or currency, coins, paper money, etc
Nymph: seductive or lustful woman, fairy
Nymphet: pubescent girl regarded as sexually desirable, young, sexually precocious girl
Oasis: fertile, vibrant, or green spot in a desert or wasteland
Objet d’art: object of art, valuable or highly artistic piece or work
Oblivion: condition or quality of being completely forgotten, void, forgetfulness
Obsequious: fawning, sycophantic, servile
Obsidian: volcanic glass of a black shade

Ocelot: undomesticated cat, like a small leopard
Odalisque: female servant, female servant in a harem
Oeillade: an amorous glance, ogle
Oeuvre: the corpus of an author, canon, or a collective symposium
Oleander: type of flower
Opacity: opaqueness, obscurity, impenetrability
Opalescent: milky and iridescent, shimmering with the colors of an opal
Opaque: impenetrable to light, not reflecting light, difficult to explain or understand
Ophidian: snake-like, like, shaped like, or relating to snakes
Opulence: wealth, affluence, great abundance, profusion, pretentiousness
Opusculum: minor work of literature
Orbital: of, pertaining to, or relating to an orbit
Orchestra: large group of musicians with a variety of instruments
Oscillate: to swing in an uninterrupted motion
Ossuary: place, container or receptacle for holding the bones of the dead
Otiose: indolent, lazy, serving no useful purpose, futile, being a leisure
Oubliette: dungeon with only opening at the top