> A thing that has already happened or been decided before those affected hear about it, leaving them with no option but to accept it.
> A thing accomplished and presumably irreversible
This is derived from the same French word which means accomplished fact which can’t be reversed.
Example
The results were presented to shareholders as a fait accompli
By the time we learned about the decision, it was already a fait accompli
Trump has shown no signs of reneging (go back on a promise / contract / undertaking) on his claims that the election was stolen, but outside his campaign, Biden’s victory has been accepted as a fait accompli
The policy change was presented to us as a fait accompli without consultation or discussion.