1 essential or needed in order to do something, provide something, or make something happen
I don’t want to be disturbed unless it’s absolutely necessary.
necessary for: basic foods regarded as necessary for health
necessary for: What type of clothing is necessary for survival at these altitudes?
it is necessary for someone to do something: It was necessary for all students to register a week in advance.
if necessary: I can take your place at the meeting tomorrow if necessary.
as necessary: We’ll be adding more workers as necessary (=as they are needed).
Synonyms and related words