isopiestic line vs isarithm

isopiestic line and isarithm both are nouns.

Word	Noun	Adjective	Verb	Adverb
isopiestic line	Yes	No	No	No
isarithm	Yes	No	No	No

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

isopiestic line: a line on a map connecting places with equal ground water pressure.
isarithm: a line drawn on a map connecting points having the same numerical value of some variable

Other hypernyms of isopiestic line include isogram, isopleth.

isopiestic line (noun)	isarithm (noun)
a line on a map connecting places with equal ground water pressure.	a line drawn on a map connecting points having the same numerical value of some variable