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• oeuvre
• oaf
• oak
• oar
• oasis
• oasthouse
• obese
• obey
• obfuscate
• obituary
• object
• objurgate
• oblation
• oblige
• obliterate
• obnoxious
• oboe
• obscure
• obsequious
• observe
• obstetric
• obstruct
• obtain
• obtuse
• ocarina
• occasion
• occult
• occupy
• occur
• ocean
• oche
• October
• ocular
• odd
• ode
• odontology
• odour
• oenology
• oestrus
• of
• off
• offal
• offend
• offer
• office
• often
• oil
• OK
• old
• olfactory
• olive
• ombudsman
• omelette
• omen
• on
• onager
• once
• one
• onion
• only
• onyx
• open
• operate
• opinion
• opium
• opossum
• opportunity
• oppose
• oppress
• opt
• optical
• optimism
• option
• opulent
• opus
• or
• oracle
• oral
• orange
• orang-utan
• orator
• orbit
• orchard
• orchestra
• orchid
• ordain
• ordeal
• order
• ordinary
• ordination
• ore
• organ
• orgy
• orient
• orifice
• origin
• orison
• ormolu
• ornament
• orthodox
• Oscar
• oscillate
• osculate
• osprey
• ostensible
• ostler
• ostracism
• ostrich
• other
• otiose
• otter
• ought
• ounce
• our
• oust
• out
• outfit
• outrage
• outstrip
• ovary

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因篇幅關系，字母O開頭的單詞只列出前 120 個；字母O開頭的英語單詞由顧邦查字典提供查詢