noun, feminine/kɔ̃.di.sjɔ̃ si.ne kwa nɔn/plural: conditions sine qua non
condition sine qua non is feminine in French.
a sine qua non, an indispensable condition
“Near-synonym: condition nécessaire”
Synonyms: condition nécessaire
Learned borrowing from Latin sine quā nōn (“without which it is not possible”).