1 planning permission is necessary I don't want to go unless it's absolutely necessary
obligatory, requisite, required, compulsory, mandatory, imperative, demanded, needed, called for, needful; essential, indispensable, vital, of the essence, incumbent; Frenchde rigueur
[Antonyms] unnecessary non-essential dispensable
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Choose the right word
necessary, requisite, essential, indispensable
Something that is necessary must be accepted or done, whether we like it or not. The word denotes something without which a condition cannot be fulfilled, often something that is needed for a particular purpose, rather than generally ( carrying out the necessary repairs | a general election was necessary). Necessary is the only one of these words that can be used in the phrase if necessary ( do a dummy run if necessary).Requisite has a very similar meaning to necessary, but it is more formal and often refers to something required by regulations rather than an inherent need ( each event must be staffed by the requisite number of officials). Unlike the other three words here, requisite is almost always used before its noun.Essential is the strongest way to say that something is necessary ( it is essential to keep up-to-date records). Some uses merge with the older meaning of ‘fundamental to the nature of something’ ( fibre is an essential ingredient of our diet): see inherent. Of these four words, it is normal to use only essential or necessary with the anticipatory subject it in a construction such as it is essential to read a daily newspaper.Indispensable is typically used of someone or something that is already present, and implies contemplation of having to do without them ( you've been absolutely indispensable to me | electricity is an indispensable source of energy which we take for granted in our everyday lives).