[William Cloud Hicklin]

Well, as CT commented with regard to a possible link between the athel- in athelas and Anglo-Saxon æðele "noble, royal" - it wouldn't have still been an Anglo-Saxon word by the time he was done with it! Rather like A-S ent "giant" became something rather different....

I think the history of "Isengard" is well enough attested that it's pointless to look around for alternate histories. AFAIK Tolkien only ever lifted one name wholesale from a RW language, aside from Shire/Bree names (and The Hobbit's dwarf-names), and that back at the very beginning: Earendel. This isn't to say that certain elements weren't borrowed: ond "stone" he consciously used, as being what apparently is the only known word from the language of Britain's pre-Celtic inhabitants. And he admitted that he might have subconsciously been influenced by Gaelic nasc ("ring," but also "bond") when BS nazg came to him.