So a pound is still a note! (3)
I believe the answer is:
sol
'so' is the definition.
(synonyms)
'a pound is still a note' is the wordplay.
I cannot quite see how this works, but
'pound' could be 'l' (abbreviation e.g. Lsd - pounds, shillings, pence) and 'l' is located in the answer.
'note' could be 'so' (musical note) and 'so' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sol that I've seen before include "Fifth note of scale" , "Note, old french coin" , "Roman sun-god" , "Note; Peruvian currency" , "Note - colloid - the Sun" .)