What category of adjectives is this? i.e. adjectives entirely unlike their nouns
Consider the noun "Jupiter", either the Roman god or the giant gaseous planet in our Solar System.
The adjective is "jovian", entirely unrelated.
Is this a distinct class of adjectives? I suspect there are many more examples.
EDIT: Is it possible that "Jupiter" does not have an adjective? "Jupiterian"?
In most studies for astrophysics I've seen, the go-to adjective is "Jovian"....
These are called collateral adjectives. You can read about them on Wikipedia and check out a list of them on Wiktionary.