isotach vs isarithm

isotach and isarithm both are nouns.

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

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

isotach: a line joining points with constant wind speed.
isarithm: a line drawn on a map connecting points having the same numerical value of some variable

Other hypernyms of isotach include isogram, isopleth.

isotach (noun)	isarithm (noun)
a line joining points with constant wind speed.	a line drawn on a map connecting points having the same numerical value of some variable