1
- required to be done, achieved, or present; needed; essential必要的; 必须的; 必需的; 根本的：
they granted the necessary planning permission
他们批准了必需的规划许可
it's not necessary for you to be here.
你没必要到这里来。
2
- determined, existing, or happening by natural laws or predestination; inevitable必然的; 不可避免的：
a necessary consequence.
必然的结果。
2.1
- Philosophy (of a concept, statement, judgement, etc.) inevitably resulting from or produced by the nature of things, so that the contrary is impossible【哲】（观念、陈述或判断等）具有必然性的。
2.2
- Philosophy (of an agent) having no independent volition【哲】（行为者）迫不得已的, 非做不行的, 非自愿的。
(一般作necessaries)(亦作necessaries of life)
1- the basic requirements of life, such as food and warmth生活必需品。
1.1
the necessary
informal an action or item needed for a purpose〈非正式〉必须做的事; 必需品：see when they need a tactful word of advice or encouragement and do the necessary.
注意他们何时需要巧妙的告诫或鼓励, 然后做该做的事。
1.2
the necessary
Brit. informal enough money for a particular purpose〈英, 非正式〉足够的钱。
短语
a necessary evil
- something that is undesirable but must be accepted不想要但又必须接受的事物。
词源
late Middle English; from Latin necessarius, from necesse 'needful'.