Probably "Castra" Arabicized = "Qasr", eh?
Yup, that's what I'd kinda thought (probably the same for the German word, Latin route), and that's what the wiki-wacky page sez. I've been wondering if Kasserine Pass (site of a US defeat in WWII) may have its roots in Qasr / castra as well. Probably not though, unless it's indirect.