Indefinable quality ( French ) (2,2,4,4)

I believe the answer is:

je ne sais quoi

(Other definitions for je ne sais quoi that I've seen before include "Indefinable quality" , "Indescribable quality" , "Quality that can't be easily described" , "(A certain) something" , "Special unknown ingredient" .)

I've seen this clue in The Independent.

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