...lacking heart, no thanks to a Parisian! (9)
I believe the answer is:
merciless
'parisian' is the definition.
Although both the answer and definition are adjectives, I don't understand how they can define each other.
'lacking heart no thanks' is the wordplay.
I cannot quite see how this works, but
'lacking' could be 'less' (I've seen this in another clue) and 'less' is found within the answer.
The remaining letters 'merci' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'to a' is the link.
Can you help me to learn more?
(Other definitions for merciless that I've seen before include "Ruthless" , "Uncharitable" , "Showing no compassion" , "Totally unforgiving" , "Cruel" .)