| Latin | Translation | Notes |
| O Deus Ego Amo Te | O God I Love You | attributed to Saint Francis Xavier |
| O fortunatos nimium sua si bona norint, agricolas | The farmers would count themselves lucky, if only they knew how good they had it | from Virgil in The Georgics, 458 |
| o homines ad servitutem paratos | Men ready to be slaves! | attributed (in Tacitus, Annales, III, 65) to the Roman Emperor Tiberius, in disgust at the servile attitude of Roman senators; said of those who should be leaders but instead slavishly follow the lead of others |
| O tempora, o mores! | Oh, the times! Oh, the morals! | also translated "What times! What customs!"; from Cicero, Catilina I, 2 |
| Obedientia civium urbis felicitas | The obedience of the citizens makes us a happy city | Motto of Dublin |
| obiit (ob.) | one died | "He/she died", inscription on gravestones; ob. also sometimes stands for obiter (in passing or incidentally) |
| obit anus, abit onus | The old woman dies, the burden is lifted | Arthur Schopenhauer |
| obiter dictum | a thing said in passing | in law, an observation by a judge on some point of law not directly relevant to the case before him, and thus neither requiring his decision nor serving as a precedent, but nevertheless of persuasive authority. In general, any comment, remark or observation made in passing |
| obliti privatorum, publica curate | Forget private affairs, take care of public ones | Roman political saying which reminds that common good should be given priority over private matters for any person having a responsibility in the State |
| obscuris vera involvens | the truth being enveloped by obscure things | from Virgil |
| obscurum per obscurius | the obscure by means of the more obscure | An explanation that is less clear than what it tries to explain; synonymous with ignotum per ignotius |
| obtorto collo | with a twisted neck | unwillingly |
| oculus dexter (O.D.) | right eye | Ophthalmologist shorthand |
| oculus sinister (O.S.) | left eye |
| oderint dum metuant | let them hate, so long as they fear | favorite saying of Caligula, attributed originally to Lucius Accius, Roman tragic poet (170 BC); Motto of the Russian noble family Krasnitsky |
| odi et amo | I hate and I love | opening of Catullus 85; the entire poem reads, "odi et amo quare id faciam fortasse requiris / nescio sed fieri sentio et excrucior" (I hate and I love. Why do I do this, you perhaps ask. / I do not know, but I feel it happening to me and I am burning up.) |
| odi profanum vulgus et arceo | I hate the unholy rabble and keep them away | from Horace |
| odium theologicum | theological hatred | name for the special hatred generated in theological disputes |
| oleum camino | (pour) oil on the fire | from Erasmus' (1466–1536) collection of annotated Adagia |
| omne ignotum pro magnifico | every unknown thing [is taken] for great | or "everything unknown appears magnificent" The source is Tacitus: Agricola, Book 1, 30 where the sentence ends with 'est'. The quotation is found in Conan Doyle's Sherlock Holmes story 'The Red-Headed League' where the 'est' is missing. |
| omne initium difficile est | every beginning is difficult | |
| omne vivum ex ovo | every living thing is from an egg | foundational concept of modern biology, opposing the theory of spontaneous generation |
| Omnes homines sunt asini vel homines et asini sunt asini | All men are donkeys or men and donkeys are donkeys | a sophismata proposed and solved by Albert of Saxony (philosopher) |
| omnes vulnerant, postuma necat or omnes feriunt, ultima necat | all [the hours] wound, last one kills | usual in clocks, reminding the reader of death |
| omnia cum deo | all with God | motto for Mount Lilydale Mercy College, Lilydale, Victoria, Australia |
| omnia dicta fortiora si dicta Latina | everything said [is] stronger if said in Latin | or "everything sounds more impressive when said in Latin"; a more common phrase with the same meaning is quidquid Latine dictum sit altum videtur (whatever said in Latin, seems profound) |
| omnia extares! | Interpreted as "Let it all hang out!", but in fact incorrect Latin construction with no real meaning[1] | motto for The Evergreen State College, Olympia, Washington, USA[2] |
| omnia in mensura et numero et pondere disposuisti | Thou hast ordered all things in measure, and number, and weight. | Book of Wisdom, 11:21 |
| omnia mutantur, nihil interit | everything changes, nothing perishes | Ovid (43 BC – 17 AD), Metamorphoses, book XV, line 165 |
| omnia omnibus | all things to all men | 1 Corinthians 9:22 |
| si omnia ficta | if all (the words of poets) is fiction | Ovid, Metamorphoses, book XIII, lines 733–4: "si non omnia vates ficta" |
| omnia vincit amor | love conquers all | Virgil (70 BC – 19 BC), Eclogue X, line 69 |
| omnia munda mundis | everything [is] pure to the pure [men] | from The New Testament |
| omnia praesumuntur legitime facta donec probetur in contrarium | all things are presumed to be lawfully done, until it is shown [to be] in the reverse | in other words, "innocent until proven guilty" |
| omnis vir enim sui | Every man for himself! | |
| omnibus idem | the same to all | motto of Pieter Corneliszoon Hooft, usually accompanied by a sun, which shines for (almost) everyone |
| omnibus locis fit caedes | There is slaughter everywhere (in every place) | Julius Caesar's The Gallic War, 7.67 |
| omnis traductor traditor | every translator is a traitor | every translation is a corruption of the original; the reader should take heed of unavoidable imperfections |
| omnis vir tigris | everyone a tiger | motto of the 102d Intelligence Wing |
| omnium gatherum | gathering of all | miscellaneous collection or assortment; "gatherum" is English, and the term is used often used facetiously |
| onus probandi | burden of proof | |
| onus procedendi | burden of procedure | burden of a party to adduce evidence that a case is an exception to the rule |
| opera omnia | all works | collected works of an author |
| opera posthuma | posthumous works | works published after the author's death |
| operari sequitur esse | act of doing something follows the act of being | scholastic phrase, used to explain that there is no possible act if there is not being: being is absolutely necessary for any other act |
| opere citato (op. cit.) | in the work that was cited | used in academic works when referring again to the last source mentioned or used |
| opere et veritate | in action and truth | doing what you believe is morally right through everyday actions |
| opere laudato (op. laud.) | | See opere citato |
| operibus anteire | leading the way with deeds | to speak with actions instead of words |
| ophidia in herba | a snake in the grass | any hidden danger or unknown risk |
| opinio juris sive necessitatis | an opinion of law or necessity | a belief that an action was undertaken because it was a legal necessity; source of customary law |
| opus anglicanum | English work | fine embroidery, especially used to describe church vestments |
| Opus Dei | The Work of God | Catholic organisation |
| ora et labora | pray and work | This principle of the Benedictine monasteries reads in full: "Ora et labora (et lege), Deus adest sine mora." "Pray and work (and read), God is there without delay" (or to keep the rhyme: "Work and pray, and God is there without delay") |
| ora pro nobis | pray for us | "Sancta Maria, mater Dei, ora pro nobis pecatoribus" |
| orando laborando | by praying, by working | motto of the Rugby School |
| oratio directa | direct speech |
expressions from Latin grammar |
| oratio obliqua | indirect speech |
| orbis non sufficit | the world does not suffice or the world is not enough | from Satires of Juvenal (Book IV/10), referring to Alexander the Great; James Bond's adopted family motto in the novel On Her Majesty's Secret Service; it made a brief appearance in the film adaptation of the same name and was later used as the title of the nineteenth James Bond film, The World Is Not Enough. |
| orbis unum | one world | seen in The Legend of Zorro |
| ordo ab chao | out of chaos, comes order | one of the oldest mottos of Craft Freemasonry.[3] |
| (oremus) pro invicem | (Let us pray), one for the other; let us pray for each other | Popular salutation for Roman Catholic clergy at the beginning or ending of a letter or note. Usually abbreviated OPI. ("Oremus" used alone is just "let us pray"). |
| orta recens quam pura nites | newly risen, how brightly you shine | Motto of New South Wales |