stiffness vs strictness

stiffness and strictness both are nouns.

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

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

Other hypernyms of stiffness include sternness.

stiffness (noun)	strictness (noun)
the physical property of being inflexible and hard to bend	uncompromising resolution
the property of moving with pain or difficulty	conscientious attention to rules and details
the inelegance of someone stiff and unrelaxed (as by embarrassment)
excessive sternness
firm resoluteness in purpose or opinion or action