Implacable, no thanks to the French? (9)
I believe the answer is:
merciless
'implacable' is the definition.
(associated in meaning)
'no thanks to the french?' is the wordplay.
I cannot really see how this works, but
'the french?' could be 'les' (plural form of 'the' in French) and 'les' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for merciless that I've seen before include "Ruthless" , "Totally unforgiving" , "Uncharitable" , "Showing no compassion" , "Cruel" .)