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' says the answer is hidden in the clue.
'enesse' can be found hidden inside 'pureness evidently'.
'enesse' in reverse letter order is 'ESSENE'.
'contributing to' is the 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" .)