what the difference between vital, essential, critical, crucial, imperative?
All of these describe something are important and urgent, so how could I use these words in different situations?

Question

Answer

They all mean the same thing and could be used interchangeably in most situations.

It is vital/critical/imperative/crucial/critical/essential that we talk today.

But I don't think imperative works as well as an adjective.  For example,
He just had a vital meeting with his bank.
He just had an imperative meeting with his bank. - this sound wrong to me.