thirsty vs thirstiness

thirsty is not a noun while thirstiness is a noun.

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

thirsty (noun)	thirstiness (noun)
	strong desire for something (not food or drink)
	a physiological need to drink
	a deficiency of moisture (especially when resulting from a permanent absence of rainfall)

thirsty (adjective)	thirstiness (adjective)
feeling a need or desire to drink
able to take in large quantities of moisture
(usually followed by `for') extremely desirous
needing moisture