Singing voice of a very special tomcat (4)
I believe the answer is:
alto
'singing voice' is the definition.
(type of singing voice)
'of a very special tomcat' is the wordplay.
'of' indicates a hidden word.
'ALTO' is hidden within 'very special tomcat'.
(Other definitions for alto that I've seen before include "Low female singing voice" , "High male singing voice" , "The highest adult male singing voice" , "Lowest female singing voice" , "Key old > male who scores high" .)