'OK'
I visited Ireland many years ago, and I noticed how all the older Irish folk would signal agreement with what sounded like "OK" with a thicker-than-usual accent (often accompanied with a kind of snort/throat-clearing noise). I commented on it to my Irish wife, and she explained that what they were really saying was "och aye", literally "oh yes" in Gaelic. Given how many Irishmen have come to America, I'd give the Irish credit for "OK".
--Robert