Zealot contributing to upturn in pureness evidently (6)
I believe the answer is:
essene
'zealot' is the definition.
(I've seen this before)
'upturn in pureness evidently' is the wordplay.
'upturn' is a reversal indicator (in a down clue, letters go up).
'in' indicates a hidden word.
'enesse' can be found hidden inside 'pureness evidently'.
'enesse' backwards is 'ESSENE'.
'contributing to' acts as a link.
(Other definitions for essene that I've seen before include "Zealot" , "Ascetic type" , "Early Jewish ascetic" , "Member of Dead Sea Scrolls sect" , "Old Jewish sectarian" .)