absolutely necessary
really necessary

Rest in bed is absolutely necessary for several more days even a week.

As for food they won't get any more than is absolutely necessary.

The first and second are absolutely necessary to them as men.

Absolutely necessary to make sure of him before taking a single step.

He didn't want to take any more time here than absolutely necessary.

"Free trade is absolutely necessary to the future economic well being of the world," he said.

In case it were absolutely necessary to do so, I was to tell you these words.

If absolutely necessary, she knew she'd be able to keep this up for hours.

I wouldn't tell him more about yourself than you find absolutely necessary.

"What we have done is not something I would like to do, but it was absolutely necessary."