sine qua non

something necessary, indispensable, or unavoidable <an extensive grounding in mathematics is a sine qua non for a career in architecture> Synonyms condition, demand, must, must-have, necessary, necessity, need, needful, requirement, requisite, essentialRelated Words precondition, prerequisite; advantage, edge, plus; desideration, desideratum, wishNear Antonyms amenity, comfort, extra, extravagance, frill, indulgence, luxury, superfluity, surplus, surplusageAntonyms nonessential, nonnecessity