The piano, I note, has four legs (3)
I believe the answer is:
pig
'has four legs' is the definition.
I can't tell whether this defines the answer.
'the piano i note' is the wordplay.
'the piano' becomes 'p' (musical abbreviation).
'note' becomes 'g' (musical note).
'p'+'i'+'g'='PIG'
Can you help me to learn more?
(Other definitions for pig that I've seen before include "Unforged metal" , "Sow, perhaps" , "& 16 Animal pen" , "Quantity of metal" , "Empress of Blandings?" .)