But in Old German, the prefix ir-/ur- meant "thoroughly", from Proto-Germanic uz-, meaning "out", ultimately from Proto-Indo-European úd-, meaning "outward"/"upward", which is also the origin of the English word "out", as well as the prefix "or-", as in "ordeal". Proto-Indo-European coexisted with Ur, and it doesn't really make sense that Ur would lead to the PIE prefix úd-.