tallness vs highness

tallness and highness both are nouns.

Word	Noun	Adjective	Verb	Adverb
tallness	Yes	No	No	No
highness	Yes	No	No	No

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

tallness: the vertical dimension of extension; distance from the base of something to the top
highness: the quality of being high or lofty

Other hyponyms of tallness include loftiness, lowness.

tallness (noun)	highness (noun)
the vertical dimension of extension; distance from the base of something to the top	the quality of being high or lofty
the property of being taller than average stature	a high degree (of amount or force etc.)