stern vs unrelenting

stern is a noun but unrelenting is not a noun.

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

As adjectives, stern and unrelenting are synonyms defined as:

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

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

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

stern (adjective)	unrelenting (adjective)
severe and unremitting in making demands	never-ceasing
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	punishingly harsh
severely simple