二分之一用英语可以说作 "one half". 来源是英语里表示分数的方法。例如：
One half of the pie is missing.
The recipe calls for one half cup of sugar.
The team won one half of their games this season.
英语里表示分数的方法是将分子写成整数，分母写成基数名词。例如，三分之二可以写作 "three halves" 或者 "3/2". 但是，当分子是 1 时，通常只写 "one"，而不会写成 "1/2" 或者 "one half". 例如：
One half of the class is absent today.
I only need one half of a cup of sugar for this recipe.
The team lost one half of their games this season.
请注意，这种表示法仅适用于分数的整数部分是 1 的情况。例如，如果你想表示五分之三，你不能写成 "one half"，而应该写成 "five thirds" 或者 "5/3"。例如：
Five thirds of the pizza is gone.
The recipe calls for five thirds of a cup of sugar.
The team won five thirds of their games this season.
总之，"one half" 是英语里表示二分之一的常用方法。当分数的整数部分是 1 时，可以使用这种表示方法，其他情况下应该使用普通的分数表示法。例如：
One half of the class is absent today.
The recipe calls for five thirds of a cup of sugar.
The team won one half of their games this season.