Ars Goetia is a well-known book about demonology written in Mediaeval Latin. I'm having trouble analyzing the grammatical structure of the title. Ars is a feminine noun in the singular nominative form. Goetia looks like it is feminine and in the singular nominative form. However, I'm not sure how it relates grammatically to Ars.
I looked up the entry for ars in Lewis and Short, and it seems to say that it is generally modified by an adjective (e.g. ars gymnastica) or a noun in the genitive case (e.g. ars disserendi). Goetia is obviously not a genitive form, but I also wouldn't think it would be used as an adjective: it's a loanword from the Greek noun γοητεια (I would expect the corresponding adjective to be something like Goeticus/-um/-a).
To me, it seems like it is an appositive noun. Am I right? If so, are there examples of this construction being used with ars in Classical Latin? And are there any differences in meaning, or other reasons to use the title Ars Goetia instead of Ars Goetiae or Ars Goetica?
One reason I suspect the author intentionally used an appositive noun after ars here is because a few of the other books in the Lesser Key of Solomon also seem to be titled this way, such as "Ars Theurgia-Goetia" and "Ars Almadel." But there is also a book that seems to have the structure with an adjective, the "Ars Paulina."