under no circumstances, absolutely not, no way (Super common in sentences and as a stand alone.)
Opposite (closest): auf jeden Fall
The core idea of this root was:
It doesn’t have any other relatives besides to fall and fallen (and “to fell” and “fällen”) in German and English and it is notably absent from the Latin branch of the Indo-European family. There, the word for falling was *kadere, which is the origin of words like cadence, incident or case.