Key is, with hesitation, reversed in organised sound (5)
I believe the answer is:
music
'organised sound' is the definition.
(I've seen this before)
'key is with hesitation reversed' is the wordplay.
'key' becomes 'c' (musical key).
'with' says to put letters next to each other.
'hesitation' becomes 'um' (um is said in hesitation).
'reversed' says the letters should be written backwards.
'c'+'is'+'um'='cisum'
'cisum' in reverse letter order is 'MUSIC'.
'in' acts as a link.
(Other definitions for music that I've seen before include "Pleasant sound (to one's ears)" , "'My - - ' , radio quiz" , "Pleasing sound" , "Organised notes (that must sometimes be faced)" , "Audible art form ..." .)