Crossword Genius

Naïf, amazingly, exposes regressively ruthless organisation (5)

Ross

I believe the answer is:

mafia

I'm a little stuck... Click here to teach me more about this clue!

'ruthless organisation' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'naif amazingly exposes regressively' is the wordplay.
'MAFIA' is hidden backwards in amongst the letters.
However, I am uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for mafia that I've seen before include "Secret criminal organisation" , "Criminal organisation also known as Cosa Nostra" , "Sicilian one" , "Sicilian criminal body" , "Gangsters" .)

I've seen this clue in The Irish Times.
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