Sound unit last month initially avoided calumny (7)
I believe the answer is:
decibel
'sound' is the definition.
I know that 'sound' relates to this answer. I also know that both the answer and definition are singular nouns
'unit last month initially avoided calumny' is the wordplay.
'unit' becomes 'I' (resembles b, a unit).
'last month' becomes 'dec' (short for December, last month of the year).
'initially' says to put letters next to each other (some letters go before others).
'avoided calumny' becomes 'bel' (I can't explain this - if you can you should give a lot more credence to this answer).
'i' after 'dec' is 'deci'.
'deci'+'bel'='DECIBEL'
Can you help me to learn more?
(Other definitions for decibel that I've seen before include "I relate to volume" , "Noise unit" , "Unit relating to sound or power measurement" , "Measure of noise intensity" , "Unit of measurement for loudness" .)