What is 'nor-nor-west'?
'I wondered for a while if it was that he was a little mad,' Lavinia said.
'Mad!'
'Only nor-nor-west, of course. There is an unholy attraction about people who are stark crazy in one direction but quite sane every other way.'
(Chapter 6 To Love and Be Wise, http://gutenberg.net.au/ebooks08/0800551h.html#ch06)

Question

Answer

It's short for "north-north-west", ie. the direction between northwest and north.

It's a reference to Hamlet's line, "I am but mad north-north-west. When the wind is southerly, I know a hawk from a handsaw." Paraphrasing Shakespeare, the meaning is that the person is insane only in certain situations. The reference to "north-north-west" is the direction of the wind.

Answer

It's a compass direction between due north and northwest -- seldom used in everyday life. In the passage, the idea is that it is a very specific direction. The speaker is suggesting that the man is mostly sane, but that he has one particular area in which he is insane.