mercy vs free pardon

mercy and free pardon both are nouns.

Word	Noun	Adjective	Verb	Adverb
mercy	Yes	No	No	No
free pardon	Yes	No	No	No

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

mercy: leniency and compassion shown toward offenders by a person or agency charged with administering justice
free pardon: the formal act of liberating someone

Other hyponyms of mercy include commutation, re-sentencing, amnesty, pardon, quarter, reprieve, respite.

mercy (noun)	free pardon (noun)
leniency and compassion shown toward offenders by a person or agency charged with administering justice	the formal act of liberating someone
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