strictness vs unpermissiveness

strictness and unpermissiveness both are nouns.

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

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

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

Other hypernyms of strictness include restrictiveness.

strictness (noun)	unpermissiveness (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