rigour vs stiffness

rigour and stiffness both are nouns.

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

As nouns, rigour and stiffness are synonyms defined as:

Other synonyms of rigour include hardness, harshness, inclemency, rigor, rigorousness, rigourousness, severeness, severity.

rigour (noun)	stiffness (noun)
something hard to endure	the physical property of being inflexible and hard to bend
the quality of being valid and rigorous	the property of moving with pain or difficulty
excessive sternness	the inelegance of someone stiff and unrelaxed (as by embarrassment)
	excessive sternness
	firm resoluteness in purpose or opinion or action