"Being and Nothingness" author (6)
I believe the answer is:
sartre
'being and nothingness author' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sartre that I've seen before include "Jean-Paul ___, French existentialist, d. 1980" , "Arrest (anag) - French philosopher, d. 1980" , "Jean-Paul --, French author and philosopher" , "Jean-Paul -, French philosopher/author" , "Jean-Paul -, Fr. author" .)