First-century mystic (6)
I believe the answer is:
essene
'first-century mystic' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for essene that I've seen before include "Zealot" , "Ancient Jewish ascetic sect member" , "Old Jewish sectarian" , "Member of Dead Sea Scrolls sect" , "Jewish frater" .)