An essential for the Latinist (4,3,3)

I believe the answer is:

sine qua non

'an essential for the latinist' is the definition.
(Latin phrase meaning something essential)

This is all the clue.

(Other definitions for sine qua non that I've seen before include "Must" , "Indispensable condition" , "A vital qualification" , "Essential condition" .)

I've seen this clue in The Guardian.

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