A male homosexual. A bit like pufter, but with an 'N' at the beginning. Used in southern England.
Dude to Girlfriend: "Who was that guy I saw you talking to?"
Girlfriend to Dude: "Oh him, don't worry, he's a raving nufter".
(Later) Dude to Nufter: "Fancy a threesome, nufter?"
Nufter to Dude: "You nufter".