Brace is appropriate in audition (5)
I believe the answer is:
steel
'brace' is the definition.
(I know that steel is a more specific form of brace)
'appropriate in audition' is the wordplay.
'appropriate' becomes 'steal' (appropriate can mean to steal).
'in audition' shows a homophone (sound like) (audition can mean hearing).
'steal' is a homophone of 'STEEL'.
'is' acts as a link.
(Other definitions for steel that I've seen before include "brace" , "nerve" , "Strong metal" , "Strength, determination" , "Determination, metal" .)