tenseness vs tonus

tenseness and tonus both are nouns.

Word	Noun	Adjective	Verb	Adverb
tenseness	Yes	No	No	No
tonus	Yes	No	No	No

As nouns, tonus is a hyponym of tenseness; that is, tonus is a word with a more specific, narrower meaning than tenseness:

tenseness: the physical condition of being stretched or strained
tonus: the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli

Other hyponyms of tenseness include tone, tonicity.

tenseness (noun)	tonus (noun)
the physical condition of being stretched or strained	the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli
(psychology) a state of mental or emotional strain or suspense