My understanding is that it is an English word, outwi being the Scots equivalent.
I once, while leaning on a gate in Suffolk, heard a rustle to my right. There was a strong gale, blowing in my face. I looked down and an otter emerged from some shrubbery and sat on my right foot. She couldn't smell me and hadn't seen me.
Sadly, in such an exciting moment, I twitched and she was away down into the adjacent dyke, coming up some way away under a terrified Moorhen and then away again.