Byzantine patterns in part of church (8)
I believe the answer is:
transept
'part of church' is the definition.
('transept' is part of 'church')
'byzantine patterns' is the wordplay.
'byzantine' is an anagram indicator.
'patterns' is an anagram of 'TRANSEPT'.
'in' acts as a link.
(Other definitions for transept that I've seen before include "Part of church off aisle" , "Crossing part of a church" , "Something dividing church in two" , "Part of a church - patterns (anag)" , "Arm of church body" .)