hypotonicity vs tonus

hypotonicity and tonus both are nouns.

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

As nouns, tonus is a hypernym of hypotonicity; that is, tonus is a word with a broader meaning than hypotonicity:

hypotonicity: (of muscular tissue) the state of being hypotonic
tonus: the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli

Other hypernyms of hypotonicity include tone, tonicity.

hypotonicity (noun)	tonus (noun)
(of muscular tissue) the state of being hypotonic	the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli
(of a solution) the extent to which a solution has a lower osmotic pressure than some other