Thanks much, useby and pootle. Sadly only confirms my "fit head."
I was apparently on the wrong track with "One from Thurso" and "Drug needles," will have to go back to the drawing board on those.
Useby, re: sieges—That was an idea I had at one point, and my strongest suspicion was around an avian usage, which led to a lot of googling but I couldn't find anything useful so eventually gave up on that line of pursuit.
Pootle, re: South Burmese—My potential answers also use "axe" as definition. They follow the same track, perhaps this will help you (or demonstrate why my answers are in fact wrong!):
South is the usual. Burmese title is a single letter, best known for its use by a former UN Secretary General. The title is enclosed by "bit". I have several candidates for this word, depending on what the discarded letter is; they ultimately result in one of two answers, each of which plausibly means "axe." The most promising candidate has an equine usage, but I'm slightly sceptical because it would make the excess letter redundant in a way that nullifies an entire component of the wordplay, and I'm not sure if that's kosher.