strictness vs restrictiveness

strictness and restrictiveness both are nouns.

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

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

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

Other hypernyms of strictness include unpermissiveness.

strictness (noun)	restrictiveness (noun)
uncompromising resolution	a lack of permissiveness or indulgence and a tendency to confine behavior within certain specified limits
conscientious attention to rules and details	a grammatical qualification that makes the meaning more specific (`red hat' has a more specific meaning than `hat')