Sinatra when performing, a master of his craft (7)
I believe the answer is:
artisan
'a master of his craft' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'sinatra when performing' is the wordplay.
'when performing' is an anagram indicator (the letters move around or 'perform').
'sinatra' anagrammed gives 'ARTISAN'.
Can you help me to learn more?
(Other definitions for artisan that I've seen before include "one in command of craft?" , "Skilled tradesman" , "Technician" , "Journeyman" , "Skilled worker or craftsman" .)