Key passage for the audience (4)
I believe the answer is:
isle
'key' is the definition.
(thesaurus)
'passage for the audience' is the wordplay.
'passage' becomes 'aisle' (aisle is a kind of passage).
'for the audience' shows a homophone (sound like).
'aisle' sounds like 'ISLE'.
(Other definitions for isle that I've seen before include "Detached place" , "Small mass of land in the sea" , "Eg, eyot or inch" , "Could be Man" , "'This scepter'd - - (Shakespeare)" .)