Unforgiving Old Testament so defective? (8)
I believe the answer is:
ruthless
'unforgiving' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ruthless that I've seen before include "nasty" , "Hustlers can be without mercy" , "Harsh" , "Callous" , "Without pity, merciless" .)