severeness vs stiffness

severeness and stiffness both are nouns.

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

As nouns, severeness and stiffness are synonyms defined as:

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

severeness (noun)	stiffness (noun)
extreme plainness	the physical property of being inflexible and hard to bend
excessive sternness	the property of moving with pain or difficulty
something hard to endure	the inelegance of someone stiff and unrelaxed (as by embarrassment)
used of the degree of something undesirable e.g. pain or weather	excessive sternness
	firm resoluteness in purpose or opinion or action