unrelenting vs stern

unrelenting is not a noun while stern is a noun.

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

As adjectives, unrelenting and stern are synonyms defined as:

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

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

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

unrelenting (adjective)	stern (adjective)
never-ceasing	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
punishingly harsh	of a stern or strict bearing or demeanor; forbidding in aspect
	severely simple