1 [U] necessity (for sth/to do sth) the need for sth; the fact that sth must be done or must happen 需要；必要性: Is there any necessity for change? 是否有必要更改？There's no necessity to write every single name down. 不必把所有名字都一一写下来。They sold the car out of necessity (= because they had to). 他们不得不把汽车卖了。

2 [C] something that you must have 必要的东西；必需品: Clean water is an absolute necessity. 清洁的水是不可或缺的东西。