The quality of mercy (8)
I believe the answer is:
leniency
I believe this is a double definition.
'the quality' is the first definition.
(leniency is a kind of quality)
'mercy' is the second definition.
(I know that leniency is a type of mercy)
'of' acts as a link.
(Other definitions for leniency that I've seen before include "Mercifulness" , "Mildness and tolerance" , "The quality of mercy" , "Mercy, tolerance" , "Clemency, tolerance" .)