When quietly furious, breathe audibly (8)
I believe the answer is:
aspirate
'breathe audibly' is the definition.
'aspirate' can be an answer for 'breathe' (thesaurus). I am not sure about the 'audibly' bit.
'when quietly furious' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'quietly' becomes 'p' (p for piano and quiet).
'furious' becomes 'irate' (I've seen this before).
'as'+'p'+'irate'='ASPIRATE'
Can you help me to learn more?
(Other definitions for aspirate that I've seen before include "inhale" , "Stop" , "Hook, initially" , "roughly speaking?" , "how he lived his life" .)