Quietly lie about stack (4)
I believe the answer is:
pile
'stack' is the definition.
(I know that stack can be written as pile)
'quietly lie about' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'about' indicates an anagram.
'lie' is an anagram of 'ile'.
'p'+'ile'='PILE'
(Other definitions for pile that I've seen before include "supporting column" , "Post" , "large amount of money" , "Arrange in stacks" , "large building" .)