height vs highness

height and highness both are nouns.

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

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

height: 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 height include loftiness, lowness.

height (noun)	highness (noun)
the vertical dimension of extension; distance from the base of something to the top	the quality of being high or lofty
(of a standing person) the distance from head to foot	a high degree (of amount or force etc.)
elevation especially above sea level or above the earth's surface
the highest level or degree attainable; the highest stage of development