Asian fellows taken in by heretic (8)
I believe the answer is:
armenian
'asian' is the definition.
(I know that Armenian is a type of asian)
'fellows taken in by heretic' is the wordplay.
'fellows' becomes 'men' (fellow can mean a man).
'taken in by' means one lot of letters goes inside another.
'heretic' becomes 'arian' (Arianism is a form of heresy).
'men' placed within 'arian' is 'ARMENIAN'.
(Other definitions for armenian that I've seen before include "language" , "ethnic group in Asia" , "Eg, native of Yerevan" , "Person from Yerevan, say" , "of the Southern Caucasus" .)