Definition of sine qua non noun from the Oxford Advanced Learner's Dictionary

 

sine qua non

 noun
noun
BrE BrE//ˌsɪneɪ kwɑː ˈnəʊn//
 
; NAmE NAmE//ˌsɪneɪ kwɑː ˈnoʊn//
 
 
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[singular] sine qua non (of/for something) (from Latin, formal) something that is essential before you can achieve something else TV coverage is the sine qua non of a sport if it is to thrive. Trust is a sine qua non for any counselling. Word OriginLatin, literally ‘(cause) without which not’.
See the Oxford Advanced American Dictionary entry: sine qua non