I'll be heard in the passage (5)
I believe the answer is:
'passage' is the definition.
(aisle is a kind of passage)
'i'll be heard' is the wordplay.
'be heard' indicates a 'sounds like' (homophone) clue.
'ill' sounds like 'AISLE'.
'in the' acts as a link.
(Other definitions for aisle that I've seen before include "Passage between seating areas", "Passageway between blocks of seats", "way for prospective union members?", "Passage between shelves in supermarket", "Way between seat blocks".)