a)CHANGE/MAKE something DIFFERENTif you deal with something once and for all, you deal with it completely and finally 彻底地,一劳永逸地
Let’s settle this matter once and for all.
我们把这个问题彻底解决了吧。
b)British EnglishBrE spokenTELL/ORDER somebody TO DO something used to emphasize your impatience when you ask or say something that you have asked or said many times before 最后一次〔强调不耐烦〕
Once and for all, will you switch off that television!