Not going for Greek character in song (6)

'not going' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'greek character in song' is the wordplay.
'greek character' becomes 'nu' (letter from the Greek alphabet).
'in' is an insertion indicator.
'song' becomes 'aria' (piece of music in an opera).
'nu' going into 'aria' is 'ANURIA'.

'for' is the link.

Can you help me to learn more?