vital part
vital piece
vital element
vital component
vital ingredient

I found this book in the library and it simply did not show the vital elements.

The usual measures leave out some of the most vital elements.

Position is one of the most vital elements to understand in order to be a long-term winning player.

Now she could feel the vital elements within the flow.

But how much do you really know about this vital element?

But it was a vital element in South's thoughtful plan.

Knowing where to find it was the last, vital element.

It is a vital element in a modern society and economy.

The most vital element in the future of the steel industry is research.

If that was so, then the vital element of surprise had been lost.