mercy vs forgivingness

mercy and forgivingness both are nouns.

Word	Noun	Adjective	Verb	Adverb
mercy	Yes	No	No	No
forgivingness	Yes	No	No	No

As nouns, forgivingness is a hyponym of mercy; that is, forgivingness is a word with a more specific, narrower meaning than mercy:

Other hyponyms of mercy include compassion, pity, kindness, lenience, leniency, lenity, mildness.

mercy (noun)	forgivingness (noun)
leniency and compassion shown toward offenders by a person or agency charged with administering justice	tendency to be kind and forgiving
alleviation of distress; showing great kindness toward the distressed
a disposition to be kind and forgiving
the feeling that motivates compassion
something for which to be thankful