vital part
vital piece
vital element
vital component
vital ingredient

These are the vital components of your engine's breathing system.

Clearly, the audience is a vital component of any musical event.

This is a vital component of oil and gas exploration.

There was barely enough of the vital component left for the spell.

A very vital component of all our environmental concerns is going to have to be prevention.

The canal was once a vital component of the town's economy.

So cookies are an important, and in some cases vital, component of web technology.

More often, a hot spare is a single vital component without which the entire system would fail.

We have to remember that electricity is a vital component in our economy.

A strong family unit is a vital component of a healthy society.