dry mouth vs waterlessness

dry mouth and waterlessness both are nouns.

Word	Noun	Adjective	Verb	Adverb
dry mouth	Yes	No	No	No
waterlessness	Yes	No	No	No

As nouns, waterlessness is a hypernym of dry mouth; that is, waterlessness is a word with a broader meaning than dry mouth:

dry mouth: abnormal dryness of the mouth resulting from decreased secretion of saliva
waterlessness: the condition of not containing or being covered by a liquid (especially water)

Other hypernyms of dry mouth include dryness, xerotes.

dry mouth (noun)	waterlessness (noun)
abnormal dryness of the mouth resulting from decreased secretion of saliva	the condition of not containing or being covered by a liquid (especially water)