A little lake in a quiet part of London (4)
I believe the answer is:
pond
'a little lake' is the definition.
(I've seen this in another clue)
'quiet part of london' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'part' suggests taking the first letters.
'london' becomes 'nd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'of' is 'o'.
'p'+'o'+'nd'='POND'
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for pond that I've seen before include "Himalayan country" , "Small body of water" , "Possible site for weed" , "Pool of still water" , "Small area of still water" .)