once /wʌns/ I. adv. 1.一次： He went to London once a week.他每周去一次伦敦。 2.一度，从前：Her poems were once very popular. 她的诗一度很流行。3. 用于习语 (all) at once 1.突然：All at once, I remembered.突然，我想起来了。 2.同时，一起：You can’t do two things at once.不能同时做两件事。once in a while偶尔，间或：I like a drink in the evening once in a while.我偶尔喜欢晚上喝一杯。 once more/again 再一次：Tell me just once again.你就再告诉我一次吧。 once (and) for all 一劳永逸地：put an end to that sort of thing once and for all 永远结束此类事情 once more = once again；once or twice 一两次：I have been there once or twice. 我去过那儿一两次。 once upon a time 从前(常用于讲寓言、故事的开头语) ‖II.conj.一旦…(就…)： Once you begin, you must go on. 你一旦开始，就必须继续下去。‖III. n.一次，一回： Once is enough. 一次就够了。