I think the 'very nice man' (a source of debate, in itself) Robbie was refering to, was me.
It would appear I've stirred up something of a hornets nest with this. Yes, it has been pointed out to me as pishogue/pishog (or as Darowyn spelt it 'piseog' - there are other variations too).
Put pishogue into Google and it appears to be not such a rare word at all. One definition here .
Looking at the 'official' RT web site does make me question how much input Richard Thomson has to it. The lyrics to CMM do appear to have some very un-Richard Thompson phrasing. 'Beat UP(?) the four winds ' for instance. surely the line is 'Beat AT the four winds'
I also find the fact that several people here have heard different words at that point indicates that it is not particularly clear on record (certainly not the original Fairport vinyl anyway). I've been back to both the Burland recordings (RT played on the album) and also to 'Leige and Leif' (vinyl and CD) and would have to say I can not change my mind that the word is pishogue, which make sense of the song and not 'kiss O', thistle, or mist O etc.
I have always considered RT to be an excellent and careful lyric writer, whereas some of the phases as stated on the site are sloppy. It appears to me that the site has a few mondegreens in it, from somebody who has taken words off of recordings, not the original transcripts.
I think at the end of the day we'll all just settle on our own opinions of what the words are. Ask RT, now there's a good idea!