How many letters?
At the moment, all I can think of is that it's the Ice Warriors, and they've accidentally put "fourth" instead of "third". It probably isn't, but it wouldn't be the first time they've made a cock-up with the crossword. It's really irritating, because it's more or less the only reason I still buy it these days. (I haven't got this month's yet. Didn't know it was out.)