不一定英文

That depends~~(>^ω^<)

may notEG.YaoMing may not the tallest man in china

it depends.在不同语境下有不同的回答的。。不一定就这一种。。it depends.ORZ..

uncertaintymaybe not benot necessarily例：Every rascal is not a thief,but a thief be a rascal.每个无赖不一定是盗贼;每个盗贼必定是无赖。Let's eat now and maybe we could catch a movie later. 咱们现在就吃,说不定吃完能赶场电影.Clouds do not necessarily forecast rain.云层未必预示下雨。

It depends.

Not necessarily或者necessarily都行，还是not necessarily比较准确点儿。呵呵！

not sure not certainly not always incertitude indeterminacy indetermination uncertainty unsureness

not so sure....

not neccessarilynot for sure/certaindon't count on it