hydroisohypse vs isarithm

hydroisohypse and isarithm both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydroisohypse	Yes	No	No	No
isarithm	Yes	No	No	No

As nouns, isarithm is a hypernym of hydroisohypse; that is, isarithm is a word with a broader meaning than hydroisohypse:

hydroisohypse: a line on a map connecting points of equal level on the piezometric surface.
isarithm: a line drawn on a map connecting points having the same numerical value of some variable

Other hypernyms of hydroisohypse include isogram, isopleth.

hydroisohypse (noun)	isarithm (noun)
a line on a map connecting points of equal level on the piezometric surface.	a line drawn on a map connecting points having the same numerical value of some variable