Concerned with a particular purpose; improvised.
What is ad hoc
Goodbye, until we see each other again.
What is au revoir
In extremis.
What is in extreme circumstances
Deja vu.
What is something overly familiar
I sub rosa, sneaked into the kitchen to find food at night.
What is secretly
Good faith; sincere, involving no deceit or fraud.
What is bona fides
Unorthodox, experimental.
What is avant garde
In medias res.
Coup d'etat.
What is overthrow of a government by a group
I told the cashier, merci when leaving the shopping mart.
What is thank you
Seize the day.
What is carpe diem
A witty remark.
What is bon mot
In toto.
What is altogether
De rigueur.
What is proper
I pulled away my best friend to have a, tete-a-tete with her.
What is a private conversation between two people
Let the buyer beware.
What is caveat emptor
Unlimited authority.
What is carte blanche
What is a method of procedure
Coup de grace.
What is a decisive finished blow
In reality, actually existing
What is de facto
That's life, that's how things happen.
What is c'est la vie
Modus vivendi.
What is a way of living, getting along
Fait accompli.
What is an accomplished fact, presumably irreversible