The setter will read out passage (5)
I believe the answer is:
'passage' is the definition.
(aisle can mean a path or passageway)
'the setter will read out' is the wordplay.
'the setter will' becomes 'ill' (I'll, i.e. 'the person writing the crossword will').
'read out' indicates a 'sounds like' (homophone) clue.
'ill' is a homophone of 'AISLE'.
(Other definitions for aisle that I've seen before include "The way to get married in church?" , "Division of the nave in church" , "Passage between rows of seats" , "Way between seating areas" , "way to the altar?" .)