sternness vs restrictiveness

sternness and restrictiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sternness	Yes	No	No	No
restrictiveness	Yes	No	No	No

As nouns, restrictiveness is a hypernym of sternness; that is, restrictiveness is a word with a broader meaning than sternness:

sternness: uncompromising resolution
restrictiveness: a lack of permissiveness or indulgence and a tendency to confine behavior within certain specified limits

Other hypernyms of sternness include unpermissiveness.

sternness (noun)	restrictiveness (noun)
uncompromising resolution	a lack of permissiveness or indulgence and a tendency to confine behavior within certain specified limits
the quality (as of scenery) being grim and gloomy and forbidding	a grammatical qualification that makes the meaning more specific (`red hat' has a more specific meaning than `hat')