Cruel Parisian thanks the saints (9)

I believe the answer is:

merciless

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'cruel' is the definition.
(I've seen this before)

'parisian thanks the saints' is the wordplay.
'parisian thanks' becomes 'merci' (I've seen this in another clue).
'the saints' becomes 'less' (I am not sure about this - if you are sure you should believe this answer much more).
'merci'+'less'='MERCILESS'

Can you help me to learn more?

(Other definitions for merciless that I've seen before include "Showing no compassion" , "Uncharitable" , "Cruel" , "Ruthless" , "Totally unforgiving" .)

I've seen this clue in The Daily Express.

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