One note lost in the hills; small coins remain (7)
I believe the answer is:
pennies
'coins remain' is the definition.
I can't judge whether this defines the answer.
'one note lost in the hills small' is the wordplay.
'one note' becomes 'n' (abbreviation).
'lost in' means one lot of letters goes inside another.
'the hills' becomes 'penie' (I can't explain this - if you can you should give a lot more credence to this answer).
'small' becomes 's' (abbreviation - e.g. clothes size).
'n' put into 'penie' is 'pennie'.
'pennie'+'s'='PENNIES'
(Other definitions for pennies that I've seen before include "change" , "Monetary units" .)