Punctilious, hard-hearted and hollow (5)
I believe the answer is:
niche
'hollow' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for niche that I've seen before include "Suitable spot" , "Place that's cosy" , "ideal position" , "market area for specialists" , "Nook or recess" .)