once definition: 1. one single time: 2. at the same time: 3. used when something happens that does not usually…. OneLook Thesaurus and Reverse Dictionary 18,955,870 words in 1061 dictionaries indexed — Today's word is asio Reverse Dictionary Browse Dictionaries Help Define once. Another word for at once. This is the British English definition of at once.View American English definition of at once.. Change your default dictionary to American English. At any time; ever: Once known, his face is never forgotten. At one time in the past; formerly. Search Result for "once": Wordnet 3.0. One time only: once a day. Look it up now! Look up multiple words quickly. ADVERB (3) 1. on one occasion; - Example: "once I ran into her" [syn: once, one time, in one case] 2. 2. Search once it was done and thousands of other words in English definition and synonym dictionary from Reverso. All Free. At once definition at Dictionary.com, a free online dictionary with pronunciation, synonyms and translation. 1. Simply copy and paste a list with any delimeter. Synonyms: for the last time, finally, completely, for good More Synonyms of once and for all See full dictionary entry for once COBUILD Advanced English Dictionary . one - WordReference thesaurus: synonyms, discussion and more. adv. Once in a lifetime definition at Dictionary.com, a free online dictionary with pronunciation, synonyms and translation. once synonyms, pronunciation, spelling and more from Free Dictionary. Definition and synonyms of at once from the online English dictionary from Macmillan Education.. Learn more. adv. 2. Define once more. Look it up now! once synonyms, once pronunciation, once translation, English dictionary definition of once. Meaning of once. Definition of once. 1. What does once mean? Find more ways to say at once, along with related words, antonyms and example phrases at Thesaurus.com, the world's most trusted free thesaurus. One time only: once a day. 3. Definitions/synonyms are immediately available for viewing, emailing, or downloading. 4. once more synonyms, once more pronunciation, once more translation, English dictionary definition of once more.