Increasingly fine and restrain Greek characters from the South (7)

'increasingly fine and' is the definition.
I can't tell whether this definition defines the answer.

'restrain greek characters from the south' is the wordplay.
'restrain' becomes 'rein' (reining is a kind of restraining).
'greek characters' becomes 'nus' (nu is a letter of the Greek alphabet).
'from the south' says the letters should be written backwards (in a down clue, letters go up).
'rein'+'nus'='reinnus'
'reinnus' back-to-front is 'SUNNIER'.

Can you help me to learn more?