Secretary has Byzantine-Turkish title (5)
I believe the answer is:
pasha
'turkish title' is the definition.
(I've seen this in another clue)
'secretary has byzantine' is the wordplay.
'secretary' becomes 'PA' (abbreviation for personal assistant).
'byzantine' indicates an anagram (byzantine means complex or confusing).
'has' with letters rearranged gives 'sha'.
'pa'+'sha'='PASHA'
(Other definitions for pasha that I've seen before include "Muslim dignitary" , "foreign officer" , "High ranking Turkish official or officer" , "Civil or military authority in Turkey or Egypt" , "Ottoman governor" .)