大夫 has two pronouciations, when be said "da fu", it is an official title in 3000 years ago, while be said "dai fu", it is 医生.

there meaning are the same,and they are both spoken english.in my opinion ,there differences are the time they are used. but "大夫“ has a long history,it is used from our ancient times to now. 医生 is much more younger,it is not used in our ancient times,just used now. what is more,大夫 also means a kind of official position in ancient times.

They mean the same thing. 大（dai）夫是its past name，医生则是its modern name。大部分中国人都称doctor为“医生”，不再（no longer）称“大夫”了，而且这个trend（趋势）将继续下去。“大（da）夫”还有另一个意思，是古代的一个government post（官职），但是现在也不用了。因此，你只需要记住“医生”就可以。以职业称呼，比如“某医生”和“某老师”，在中国都是a respectful form of address（尊称）。

其实都说啦！大夫（dai fu）口语化，医生更官方正式一些。

大夫 has two pronunciations, 大（da）夫 is an official position in ancient China, and 大（dai）夫 is as same as 医生，but 大夫 is informal.