Definition from macmillandictionary.com
Your browser doesn’t support HTML5 audio
I don’t want to be disturbed unless it’s absolutely necessary.
basic foods regarded as necessary for health
What type of clothing is necessary for survival at these altitudes?
It was necessary for all students to register a week in advance.
I can take your place at the meeting tomorrow if necessary.
We’ll be adding more workers as necessary (=as they are needed).
The necessary risks of medicines must be weighed against their benefits.