Quietly drag along the cavity filler (4)
I believe the answer is:
plug
'the cavity filler' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'quietly drag along' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'drag along' becomes 'lug' (I've seen this in other clues. I am not sure about the 'along' bit.).
'p'+'lug'='PLUG'
Can you help me to learn more?
(Other definitions for plug that I've seen before include "Wad of tobacco and electrical accessory" , "Stopper - advertisement" , "Bung -- promotion" , "Stopper - advert" , "Stuff" .)