O – Grammarist

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-aholic, -oholic and -holic
Abject or object
Abject vs object
Abscess vs obsess
An ounce of prevention is worth a pound of cure
Apposite vs opposite
Approbation vs opprobrium
Arcane and obsolete
Aureole vs oriole
Awed vs odd
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
Head on the chopping block and on the chopping block
Hour vs our
In over one's head or over one's head
In the cards and on the cards
In the loop and out of the loop
Include, exclude or occlude
Inpatient or outpatient
Noxious vs obnoxious
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.
Object vs object
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Obsolescent vs. obsoleteObsolete: out of date or no longer in general use.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 or ochre vs okra
Ocher vs. ochreocher in the U.S.; ochre everywhere else.
Octopi vs. octopusesThere is nothing wrong with the English plural.
Ode vs owed
Odious vs odorous
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 hook
Off the rack and off the peg
Off the record vs not for attribution
Off the wall
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 vs owe
Oh wellan interjection expressing mild disappointment.
OK vs. okayOK is the most common form.
Old chestnut
Old Glory
Old habits die hard
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 tear
On a wing and a prayer
On accident vs by accident
On cloud nine
On fleek
On one's high horse
On one’s last legs
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 burner
On the back foot
On the ball
On the bubble
On the clock
On the contrary
On the fence
On the fly
On the fritzout of order or not operating correctly.
On the house
On the lamescaped from justice or hiding from law enforcement.
On the q.t.
On the radar, off the radar, under the radar, below the radar, and above the radar
On the rocks
On the ropes
On the same page
On the straight and narrow
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 books
One for the money, two for the show
One good turn deserves another
One hand washes the other
One's eyes are bigger than one's stomach
One's name is mud
One-hit wonder
One-horse town
One-size-fits-all
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
Open and shut case
Open season
Open secret
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
Other fish to fry and bigger fish to fry
Ought vs aught
Ours is not to reason why; ours is but to do and die
Ousterthe removal of a politician or regime from power.
Out and out1. thoroughly, completely, or openly; 2. thorough, complete, or open.
Out of left field
Out of one's league
Out of pocket1. paid in cash; 2. out of reach; 3. out of money.
Out of sight, out of mind
Out of sorts
Out of the blocks and off the blocks
Out of the blue
Out of the blue vs out of the woodwork
Out of the frying pan and into the fire
Out of the woods
Out of whole cloth
Outset vs onset
Outside ofWhen outside functions as a preposition or an adverb, it doesn't need of.
Outsource
Over a barrel
Over the hill
Over the hump
Over the top
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
Overtime vs over time
Overtones vs. undertonesWhen they are synonymous with hints, suggestions, or intimations, there is not much difference between them.
Own up
Oxford comma
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
Skating on thin ice and on thin ice
Transparent, translucent and opaque
Won vs one

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