free pardon vs mercy

free pardon and mercy both are nouns.

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

As nouns, mercy is a hypernym of free pardon; that is, mercy is a word with a broader meaning than free pardon:

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

Other hypernyms of free pardon include clemency, mercifulness.

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