Hot air's circulating to plug musical release (9)
I believe the answer is:
catharsis
'release' is the definition.
(I've seen this before)
'hot air's circulating to plug musical' is the wordplay.
'hot' becomes 'h' (abbreviation eg on taps).
'circulating' is an anagram indicator.
'to plug' is an insertion indicator (to plug can mean to block a gap within something).
'musical' becomes 'Cats' (Andrew Lloyd Webber musical).
'h'+'airs'='hairs'
'hairs' is an anagram of 'harsi'.
'harsi' placed inside 'cats' is 'CATHARSIS'.
(Other definitions for catharsis that I've seen before include "purging process" , "emotional relief" , "relief of tensions" , "Release of feelings" , "emotional event" .)