sine qua non UK /ˌsaɪnɪ kweɪ ˈnɒn/US /ˌsɪni kwɑ ˈnɑn/ noun1 •An essential or indispensable element, condition, or ingredient.Literature, instead of being an accessory, is the fundamental sine qua non of complete living. — 1909 formssine qua nons · sine quibus non
