Steps -- quiet ones (5)
I believe the answer is:
paces
'steps' is the definition.
(pace is a kind of step)
'quiet ones' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'ones' becomes 'aces' ('ace' can be a synonym of 'one').
'p'+'aces'='PACES'
(Other definitions for paces that I've seen before include "Single steps" , "Steps or strides" , "Space for steps" .)