A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
- -aholic, -oholic and -holic
- Abject vs object
- Approbation vs opprobrium
- Arcane and obsolete
- Carnivore, herbivore or omnivore
- Come over vs overcome
- Covert vs overt
- Downright vs outright
- Emission vs omission
- Everyone vs every one
- Gloves are off, take the gloves off
- Hour vs our
- In over one's head or over one's head
- In the cards and on the cards
- Include, exclude or occlude
- Inpatient or outpatient
- O vs. ohO: used in classical address to invoke a person or thing. Oh: a versatile interjection expressing pain, realization, hesitation, or sorrow.
- Oar, ore and or
- Oases
- Object lessona concrete example for an abstract idea or for a lesson to guide behavior.
- Objects
- Obliged vs. obligated
- Oblique
- Obsequious
- Observance vs. observationObservance: 1. the act of complying with rule, custom, or law; 2. the act of celebrating a holiday or other ritual occasion; 3. a customary rite or ceremony.
- Obsolescent vs. obsoleteObsolete: out of date or no longer in general use. Obsolescent: becoming obsolete.
- Obstreperous
- Ocher vs. ochreocher in the U.S.; ochre everywhere else.
- Octopi vs. octopusesThere is nothing wrong with the English plural.
- Ode vs owed
- Odor vs. odourodor in the U.S.; odour everywhere else.
- Oeuvre
- Off ofThe of could usually be removed.
- Off one’s rocker and off one’s trolley
- Off the cuffunplanned.
- Off the grid or off-grid
- Off the record vs not for attribution
- Off-kilter and out of kilter
- Offal vs awful
- Offence vs. offenseoffense in the U.S.; offence everywhere else.
- OffhandOffhand: improvised or without preparation.
- OftentimesIt always bears replacement with often.
- Oh wellan interjection expressing mild disappointment.
- OK vs. okayOK is the most common form.
- Old chestnut
- Old Glory
- Old hat
- Old wives' tale vs old wise tale
- Old-fashioned or old fashion
- Oldie but goodie
- Olfactory vs old factory
- Oligarchy vs monarchy
- Olive brancha peace offering.
- Ombré ombre or hombre
- Omelet vs. omeletteomelet in the U.S.; omelette everywhere else.
- Omnibus vs ombudsman
- On a shoestring and shoestring budget
- On a wing and a prayer
- On accident vs by accident
- On cloud nine
- On fleek
- On one's high horse
- On pins and needles
- On steroidsbigger and more advanced than a previous version.
- On tenterhooksnervously waiting to find out what is going to happen in a tense or perilous situation.
- On the back foot
- On the ball
- On the bubble
- On the contrary
- On the fritzout of order or not operating correctly.
- On the lamescaped from justice or hiding from law enforcement.
- On the q.t.
- On the ropes
- On the stump and stump speech
- On the up and up1. open and honest, legitimate; 2. on the rise.
- On the wagon, off the wagonOn the wagon: not drinking. Off the wagon: drinking.
- Onboard vs. on boardOn board: aboard. Onboard: an adjective preceding the noun it modifies.
- Once in a blue moon
- Once in a lifetime vs once-in-a-lifetime
- One and the same, one in the sameOne and the same is the standard form, even if one in the same also makes sense.
- One fell swoopa single, swift action.
- One for the money, two for the show
- One's name is mud
- One-hit wonder
- One-horse town
- One-time vs. onetimeIn North America, one-time means occurring only once and onetime means former. This distinction doesn't exist outside North America.
- One-trick pony
- One-upmanshipa spirit of competition in which one tries to stay a point ahead.
- Oneself vs. one's selfOne's self works were self is meant in a psychological, spiritual, or philosophical sense. Elsewhere, the two-word form can always give way to the one-word form.
- Online vs. on-lineThe unhyphenated form is now far more common.
- Onomatopoeia
- Onusburden or responsibility.
- Oompa Loompa
- Op-ed
- Operationalise or operationalize
- Opossum vs. possumPossums are Australian. Opossums are American. Opossums are sometimes called possums.
- Oppress, repress, suppressTo oppress is to hold someone down by unjust force. To repress is to hold something back or put something down by force. To suppress is (1) to put an end to, (2) to inhibit, or (3) to keep from being revealed.
- Oracle vs auricle
- Oral vs. verbalVerbal: put in words. Oral: pertaining to the mouth.
- Ordinance vs. ordnanceOrdinance: a municipal or county law. Ordnance: weaponry.
- Organise vs. organizeorganize in the U.S. and Canada; organise is preferred outside North America.
- OrientateIt's mostly a less common variant of orient.
- Origin or origins
- Ornery
- Orthopedic vs. orthopaedic
- Ought vs aught
- Ousterthe removal of a politician or regime from power.
- Out and out1. thoroughly, completely, or openly; 2. thorough, complete, or open.
- Out of one's league
- Out of pocket1. paid in cash; 2. out of reach; 3. out of money.
- Out of sorts
- Out of the blue vs out of the woodwork
- Out of whole cloth
- Outside ofWhen outside functions as a preposition or an adverb, it doesn't need of.
- Over a barrel
- Over the hill
- Over the hump
- Over- and under- (prefixes)They can be attached to virtually any adjective or verb without requiring a hyphen.
- Overbilled vs overbuild
- Overdo vs. overdueOverdo: do to excess. Overdue: undelivered when due; late.
- Overlook vs look over
- OverlyIt can usually give way to the prefix over- which doesn't require a hyphen when attached to a common adjective.
- Overnight vs. over nightIt is one word when it functions as an adjective or an adverb.
- Overrate vs overate
- Oversee vs overlook
- Oversees vs overseas
- Overtake, take over and takeover
- Overthink vs think over
- Overtones vs. undertonesWhen they are synonymous with hints, suggestions, or intimations, there is not much difference between them.
- Oxymorona rhetorical device in which two contradictory terms are used together for emphasis or poetic effect or to arrive at a unique meaning.
- Potato and potatoes, tomato and tomatoes
- Transparent, translucent and opaque
- Won vs one