must-have vs sine qua non

must-have

noun

  • An item that one must own, or a feature that is essential to a service, etc. 

adj

  • Essential to own. 

sine qua non

noun

  • An essential or indispensable element, condition, or ingredient. 

How often have the words must-have and sine qua non occurred in a corpus of books? (source: Google Ngram Viewer )