Song performed with not so much feeling (6)
I believe the answer is:
number
'song' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for number that I've seen before include "Mathematical unit" , "One possibly" , "Count; amount" , "One may be irrational or negative" , "Digit, cipher" .)