dehydration vs thirstiness

dehydration and thirstiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
dehydration	Yes	No	No	No
thirstiness	Yes	No	No	No

As nouns, thirstiness is a hypernym of dehydration; that is, thirstiness is a word with a broader meaning than dehydration:

Other hypernyms of dehydration include thirst.

dehydration (noun)	thirstiness (noun)
the process of extracting moisture	strong desire for something (not food or drink)
dryness resulting from the removal of water	a physiological need to drink
depletion of bodily fluids	a deficiency of moisture (especially when resulting from a permanent absence of rainfall)