ne‧ces‧sa‧ry 1 S2 W1 / nesəs ə ri, nesɪs ə ri $ -seri / 形容词

1 something that is necessary is what you need to have or need to do → essential :

The booklet provides all the necessary information about the college.

No further changes were considered necessary.

absolutely/really necessary

The police are advising motorists to travel only if their journey is absolutely necessary.

it is necessary (for somebody) to do something

It’s not necessary to wear a tie.

The doctor says it may be necessary for me to have an operation.

make it necessary (for somebody) to do something

Falling profits made it necessary to restructure the business.

necessary for (doing) something

A good diet is necessary for maintaining a healthy body.

if/when/where necessary

I’ll stay up all night, if necessary, to get it finished.

Register

In everyday English, instead of saying it is necessary for somebody to do something , people usually say that someone has to do something : The doctor says it might be necessary for me to have an operation. ➔ The doctor says I might have to have an operation.

2 necessary connection/consequence etc a connection, result etc that must exist and cannot be avoided :

The closure of the factory was a necessary consequence of increased competition from abroad.

3 a necessary evil something bad or unpleasant that you have to accept in order to achieve what you want :

Mr Hurst regarded work as a necessary evil.

THESAURUS

necessary used to describe something that you need to have or do : Make sure you bring the necessary documents with you. | It may be necessary for you to have a small operation.

essential very important and necessary, especially in order to be healthy, successful etc : Vitamins are essential for healthy growth. | The tourist industry is an essential part of the Spanish economy.

vital extremely important and necessary, especially in order to avoid serious problems : A vital piece of equipment on the spacecraft had stopped operating. | It is vital that the aid is sent immediately.

compulsory if something is compulsory, you must do it because of a rule or law : Maths and Science are compulsory subjects. | All new staff undergo a compulsory training course.

obligatory if something is obligatory, you must do it because of a rule or law. Obligatory is more formal than compulsory : The use of seatbelts is obligatory. | Safety regulations have made it obligatory for all competitors to wear fist protectors.

mandatory if something is mandatory, you must do it because it is the law. Mandatory is more formal than compulsory and sounds stronger : School attendance is mandatory. | a prisoner serving a mandatory life sentence

requisite / rekwəzət, rekwɪzət / formal [通常用于名词前] the requisite things are the ones that you need to have in order to do something : The other candidates lacked the requisite skills. | the requisite evidence needed for a successful prosecution