Longman Dictionary of Contemporary English - once

~1 adv 1 »ONE TIME« on one occasion  (I've only met her once. | once before)  (Paul's been to Wexford once before.) 2 once a week/year etc one time every week etc as a regular activity  (We do aerobics once a week.) 3 at once a) immediately or without delay  (Young lady, get upstairs and clean your room at once!) b) at the same time, together  (Don't all talk at once.) 4 all at once if something happens all at once, it happens suddenly when you do not expect it  (All at once there was a loud banging on the door.) 5 once more one more time or again  (Can we go please Daddy, just once more!) 6 once again/once more again, after happening several times before  (Once again she's refusing to help.) 7 once or twice a few times  (I've driven down here once or twice before.) 8 once in a while sometimes, although not often  (It'd be nice if you'd write to me once in a while.) 9 »IN THE PAST« at some time in the past, but not now  (Franklyn had obviously been handsome once. | once-great/beautiful etc)  (It was sad to see the once-great man looking so frail.) 10 once in a blue moon informal very rarely 11 (just) for once spoken used to say that something hardly ever happens, although it should happen often  (Just for once I'd like to see him cook dinner. | Well, for once he's being nice to me.) 12 (just) this/the once spoken used to emphasize that this is the only time that you will let someone do something, or ask someone to do something  (Go on, lend me the car, just this once.) 13 once and for all a) if you deal with something once and for all, you deal with it definitely and finally  (Let's settle this matter once and for all.) b) spoken used to say that you are asking someone to do something for the last time, and they must do it  (Once and for all, will you switch off that television!) 14 once upon a time a) used at the beginning of children's stories b) spoken at a time in the past that you think was much better than now  (Once upon a time you used to be able to leave your front door unlocked.) 15 do sth once too often to be hurt because of something dangerous or stupid that you have done 16 the once spoken on one particular occasion  (I've only met her the once.) 17 once bitten, twice shy used to say that people will not do something again if it has been a bad experience ~2 conjunction from the moment that something happens  (Once she arrives, we can start. | Once in bed, the children usually stay there.)