If something is a fait accompli, it is certain to happen.
If you do something as a quid pro quo, you do it on the understanding that something will be done for you in return.
You can say vis-a-vis instead of saying "in relation to".
Something like an earthquake or a tornado can be called an act of God.
If you give someone carte blanche, you give them freedom to do whatever they want in a situation.
Your raison d'être is your reason for living, or the most important thing in your life.
If you make a volte-face, you change your opinion or your decision about something to the exact opposite of what it was.
If something is de rigeur, it is necessary to have if you want to be fashionable or be accepted into a particular social scene.
A feeling of pride and comradeship shared by members of a group such as a military unit or a sports team.