Sine qua non is a Latin phrase meaning 'WITHOUT WHICH not' and is used to refer to something that is absolutely ESSENTIAL or necessary. The term can be broken down into its component parts: sine, meaning 'WITHOUT'; qua, meaning 'WHICH'; and non, meaning 'not'. The crossword solutions for this term are MUST (4 letters), ESSENTIAL (9 letters), NECESSITY (9 letters), NEED (4 letters), CAUSA (5 letters), and ENDALL (6 letters). All of these words are synonyms for the term sine qua non, emphasizing the importance of something that is ESSENTIAL or necessary.