sine qua non

Borrowed from Latin [condiciō] sine quā nōn (“[condition] without which not”), an expression which originated in the works of Boethius as a translation of some Aristotelian expression (perhaps Ancient Greek οὗ οὐκ ἄνευ (hoû ouk áneu); compare also Modern Greek εκ των ων ουκ άνευ (ek ton on ouk ánef) / Katharevousa ἐκ τῶν ὧν οὐκ ἄνευ (ek tón ón ouk ánef)), and was later popularized by scholastics.