vital part
vital piece
vital element
vital component
vital ingredient

But he made himself a vital part of this year's fun.

He is a vital part of all the evidence for the period.

A person's home is a vital part of their lives.

It is an important industry and a vital part of our national life.

Trade talk is a vital part of the sports business.

But only stories can actually be a vital part of that care.

Training Union was a vital part of the church's program through the years until 1972.

American English didn't become a vital part of street talk.

Yet leaves are a vital part of our lives, with much to be learned about and from them.

Money sent home by these workers is a vital part of the country's economy.