unforgiving vs stern

unforgiving is not a noun while stern is a noun.

Word	Noun	Adjective	Verb	Adverb
unforgiving	No	Yes	No	No
stern	Yes	Yes	No	No

As adjectives, unforgiving and stern are synonyms defined as:

unforgiving and stern: not to be placated or appeased or moved by entreaty

Other synonyms of unforgiving include grim, inexorable, relentless, unappeasable, unrelenting.

unforgiving (noun)	stern (noun)
	the rear part of a ship
	the fleshy part of the human body that you sit on

unforgiving (adjective)	stern (adjective)
unwilling or unable to forgive or show mercy	severe and unremitting in making demands
not to be placated or appeased or moved by entreaty	not to be placated or appeased or moved by entreaty
	of a stern or strict bearing or demeanor; forbidding in aspect
	severely simple