thirst vs dehydration

thirst and dehydration both are nouns.

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

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

Other hyponyms of thirst include polydipsia.

thirst (noun)	dehydration (noun)
strong desire for something (not food or drink)	the process of extracting moisture
a physiological need to drink	dryness resulting from the removal of water
	depletion of bodily fluids

thirst (verb)	dehydration (verb)
have a craving, appetite, or great desire for
feel the need to drink