An extra bit of lustre on the piano (4)
I believe the answer is:
plus
This clue might be a double definition.
'an extra bit' is the first definition.
(I've seen this in another clue)
'lustre on the piano' is the second definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'of' acts as a link.
Can you help me to learn more?
(Other definitions for plus that I've seen before include "Advantage; also" , "As well as" , "Coupled with" , "Together with; advantage" , "Positive thing" .)