Forgiving, lenient (8)
I believe the answer is:
I believe this clue is a double definition.
'forgiving' is the first definition.
(similar in meaning)
'lenient' is the second definition.
(Other definitions for merciful that I've seen before include "Showing pity or leniency" , "Kind" , "showing forbearance" , "Clement - forbearing" , "Humane" .)