Quietly lie about big house (4)
I believe the answer is:
pile
'big house' is the definition.
(term for a large or fancy house)
'quietly lie about' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'about' is an anagram indicator.
'lie' is an anagram of 'ile'.
'p'+'ile'='PILE'
(Other definitions for pile that I've seen before include "Part of reactor" , "Large number" , "large amount of money" , "Arrange in stacks" , "Nap of a carpet" .)