Churchman one entering book emporium (6)
I believe the answer is:
bishop
'churchman' is the definition.
(I've seen this before)
'one entering book emporium' is the wordplay.
'one' becomes 'I' (Roman numeral).
'entering' means one lot of letters goes inside another.
'book' becomes 'b' (abbreviation for book).
'emporium' becomes 'shop' (I've seen this before).
'b'+'shop'='bshop'
'i' inserted within 'bshop' is 'BISHOP'.
(Other definitions for bishop that I've seen before include "He wears the mitre and carries the crozier" , "See man at the top" , "Senior church minister" , "Chess piece and senior religious person" , "Church dignitary" .)