By putting a piano key right (3)
I believe the answer is:
per
'by' is the definition.
(I've seen this in another clue)
'a piano key right' is the wordplay.
'a piano' becomes 'p' (musical abbreviation).
'key' becomes 'e' (a musical key).
'right' becomes 'r' (common abbreviation).
'p'+'e'+'r'='PER'
'putting' acts as a link.
(Other definitions for per that I've seen before include "For each or every" , "According to" , "Preposition indicating by means of" , "Preposition meaning for each" .)