Section of tranquillity we can hear (5)
I believe the answer is:
piece
'section' is the definition.
(I've seen this in another clue)
'tranquillity we can hear' is the wordplay.
'tranquillity' becomes 'peace' (peace is a kind of tranquillity).
'we can hear' indicates a 'sounds like' (homophone) clue.
'peace' sounds like 'PIECE'.
'of' acts as a link.
(Other definitions for piece that I've seen before include "king or queen?" , "Bishop, for one" , "constituent" , "Part - portion" , "Slice" .)