| object (noun) form plural: objects article, thing; goal; focus of a thought or action | object (verb) forms: objected; objected; objecting to oppose; to protest |
| objection (noun) form plural: objections opposition; appeal; denial; protest | objective (adjective) impartial; unbiased; existing outside of the mind |
| objective (noun) form plural: objectives aim; purpose, goal | obligation (noun) form plural: obligations duty responsibility; indebtedness; agreement |
| obligatory (adjective) binding; compelling; must be done; necessary | observe (verb) forms: observed; observed; observing to watch; to study; to monitor; to supervise; to discern |
| obsolete (adjective) ancient; archaic; no longer in use; outdated; useless | obtain (verb) forms: obtained; obtained; obtaining to acquire; to procure; to secure; to earn; to achieve |
| obvious (adjective) clear; unmistakable; apparent; evident; plain | obviously (adverb) clearly; unmistakably; plainly; apparently |
| occasion (noun) form plural: moccasins opportunity; occurrence, event; incident; reason; cause | occasion (verb) forms: occasioned; occasioned; occasioning to cause; to incite; to bring to pass |
| occupancy (noun) form plural: occupancies period of residence; act of taking possession (Law); right of possession | occupation (noun) form plural: occupations act of forcefully taking possession of an area; seizure; conquest; possession or settlement of land |
| occupied (adjective) conquered; seized; filled; taken up; inhabited; populated | occur (verb) forms: occurred; occurred; occurring to happen; to take place; to transpire; to come to mind; to suggest itself |
| occurrence (noun) form plural: occurrences happening; event; incident | offence (noun) form plural: offences attack; misdeed; insult; transgression |
| offender (noun) form plural: offenders transgressor; person who breaks the law; one who insults | offense (noun) form plural: offenses attack; misdeed; insult; transgression |
| offensive (noun) form plural: offensives attack; act of aggression; position of pursuit or aggression | offer (noun) form plural: offers suggestion; proposal of a price; tender; bid |
| offer (verb) forms: offered; offered; offering to suggest; to tender; to bid; to propose a price; to present | office (noun) form plural: offices chamber; bureau; incumbency; agency; authority |
| official (noun) form plural: officials person who holds public position; authority | offing (noun) form: no plural distant part of the sea visible from the shore; remote place far from the shore; high seas |
| offset (noun) form plural: offsets outcome; compensation; counterbalance | offset (verb) forms: offset; offset; offsetting to compensate; to balance |
| omission (noun) form plural: omissions deletion; negligence; failure; default | omit (verb) forms: omitted; omitted; omitting to delete; to skip over; to neglect |
| onus (noun) form plural: onuses responsibility; duty; burden; impediment; blame | operate (verb) forms: operated; operated; operating to act; to function; to manage; to use; to activate; to perform surgery |
| operation (noun) form plural: operations working, performance, handling; venture, undertaking; series of actions | operational (adjective) working; functional; ready for use |
| operator (noun) form plural: operators one who activates; worker of a telephone switchboard; operation symbol | opinion (noun) form plural: opinions attitude; outlook; formal judgment or estimation |
| opportune (adjective) appropriate; fitting; well-timed; timely; proper; expedient | opportunity (noun) form plural: opportunities chance; occasion; favorable time to act |
| opposite (adjective) facing; across from; contrary; reverse; different; antithetical | opposite (adverb) contrarily |
| opposite (noun) form plural: opposites contrast; something contrary | opposite (preposition) across from; facing |
| option (noun) form plural: options choice; alternative; possibility; selection; election | order (noun) form plural: orders arrangement; instruction; command; request for something |
| order (verb) forms: ordered; ordered; ordering to command; to request something; to arrange; to manage | ordinary (adjective) regular; common |
| ordinary (noun) form plural: ordinaries ecclesiastical judge; priest | organize (verb) forms: organized; organized; organizing to arrange; to order; to systematize; to set up; to unite; to structure |
| origin (noun) form plural: origins source; beginning; birth; parentage; nationality | original (adjective) first; primary; innovative; creative; novel |
| original (noun) form plural: originals source from which something arises; prototype; model | originality (noun) form plural: originalities state of not being a derivative of anything else |
| originally (adverb) at first; in the first place; in a unique manner | originate (verb) forms: originated; originated; originating to begin; to be created; to result from; to develop; to be produced |
| ostensibly (adverb) apparently; seemingly; to all appearances | ostentatious (adjective) showy; pretentious; bombastic; pompous; garish |
| ought (verb) form: modal verb to need to; must; to be obligated | outbound (adjective) leaving; sailing; traveling to another country |
| outdoor (adjective) of nature | outlet (noun) form plural: outlets exit; electrical source for connecting appliances; store; shop; joint |
| output (noun) form plural: outputs yield; product; manufacture; information sent out from a computer | outside (adjective) external; of the outdoors; from the outdoors; maximal |
| outside (adverb) out of doors | outside (noun) form: no plural external part or surface of something |
| outside (preposition) besides; aside from | outstanding (adjective) excellent; conspicuous; prominent; due |
| overall (noun) form plural: overalls work clothing consisting of denim trousers (usually with a bib and shoulder straps) | overcome (verb) forms: overcame; overcame; overcoming to subdue; to solve |
| overdraft (noun) form plural: overdrafts limit to which money may be withdrawn from the bank on credit | overhead (adjective) of general expenses; general |
| overhead (adverb) from above; above; in the sky | overhead (noun) form: no plural general expenses; manufacturing and business expenses |
| overlap (noun) form plural: overlaps something that is superimposed | overlap (verb) forms: overlapped; overlapped; overlapping to cover a part of; to have something in common |
| overlook (verb) forms: overlooked; overlooked; overlooking to inspect; to supervise; to miss; to omit; to ignore; to excuse | overseas (adjective) foreign; abroad |
| overseas (adverb) in a place across an ocean | oversee (verb) forms: oversaw; overseen; overseeing to supervise; to manage; to inspect |
| overt (adjective) plain; clear; visible; public; intentional; undisguised (Law) | overtime (adverb) exceeding regular working hours |
| overtime (noun) form: no plural work beyond regular working hours; pay for such work | overview (noun) form plural: overviews synopsis; general survey; introduction |
| overwhelm (verb) forms: overwhelmed; overwhelmed; overwhelming to defeat; to master; to crush; to stagger; to stun; to daze | owe (verb) forms: owed; owed; owing to be indebted to; to be under obligation to pay or repay |
| own (adjective) belonging to oneself or itself (mine, yours, his, etc.); self; by oneself | own (verb) forms: owned; owned; owning to be in possession of; to belong to; to confess |
| owner (noun) form plural: owners proprietor | ownership (noun) form plural: ownerships legal right of possession |