The most coarse to ruin chaste fashion (10)

I believe the answer is:

raunchiest

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

'the most coarse' is the definition.
I can't tell whether this definition defines the answer.

'ruin chaste fashion' is the wordplay.
'fashion' indicates anagramming the letters.
'ruin'+'chaste'='ruinchaste'
'ruinchaste' is an anagram of 'RAUNCHIEST'.

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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