Orwn.
I have always imagined a Celtic influence. In Welsh, "w" is a vowel, a sort of gentle "oo". I have always pronounced it, though, more like the Irish "aroon" as in Eileen Aroon (Eibhlín a Rún). It is a precious term of endearment.
Here is one of Dylan's less felicitous performances. Here he sings said song in Dublin and in the live recording you can clearly hear a denizen of that city cheerfully exhorting him to "feck off".
https://www.youtube.com/watch?v=S4FIf0AOv2c