Nobody heard devout woman (4)
I believe the answer is:
none
'nobody' is the definition.
(not a single person)
'heard devout woman' is the wordplay.
'heard' shows a homophone (sound like).
'devout woman' becomes 'nun' (I've seen this before).
'nun' is a homophone of 'NONE'.
(Other definitions for none that I've seen before include "Not a sausage" , "Nobody - nothing" , "Not any sort of neon" , "What's left after taking all" , "Bugger all" .)