Casting goes to one of three old comedians (6)
I believe the answer is:
stooge
'one of three old comedians' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'casting goes to' is the wordplay.
'casting' indicates anagramming the letters.
'goes'+'to'='goesto'
'goesto' anagrammed gives 'STOOGE'.
Can you help me to learn more?
(Other definitions for stooge that I've seen before include "Butt of a comic's jokes" , "Comedian's sidekick" , "Toes go wrong for the scapegoat" , "Comical straight man" , "Comedian's foil" .)