I will briefly broadcast in passageway (5)
I believe the answer is:
aisle
'passageway' is the definition.
(aisle is a kind of passageway)
'i will briefly broadcast' is the wordplay.
'i will briefly' becomes 'ill' (contraction of 'I will').
'broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'ill' sounds like 'AISLE'.
'in' acts as a link.
(Other definitions for aisle that I've seen before include "Passages between seating areas" , "Supermarket feature" , "Passageway in theatre" , "Passage between seating areas" , "Passage between shelves in supermarket" .)