mortal vs unmerciful

mortal is a noun but unmerciful is not a noun.

Word	Noun	Adjective	Verb	Adverb
mortal	Yes	Yes	No	No
unmerciful	No	Yes	No	No

mortal (noun)	unmerciful (noun)
a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

mortal (adjective)	unmerciful (adjective)
subject to death	having or showing no mercy
unrelenting and deadly
involving loss of divine grace or spiritual death
causing or capable of causing death