With your mention of the textWidth property, I thought that the less-common term (in comparison to 'width') would help pin down the issue via Google a little more easily, and so I found a blog post - http://theolagendijk.wordpress.com/2...onts-in-flash/ - which cites the difficulty of getting hold of text width properties.

I seem to have fixed my problem; it appears I wasn't embedding fonts in the necessary way, even though to all appearances embedding was working correctly. Previously, I'd created a dynamic TextField below the stage, and selected to embed a font into that. Now, I've added the font to the .fla's library, checked the box to export it for ActionScript, and created an instance of it in my Word class, and assigned its name to the font property of the TextFormat object that formats the TextField/Word. Confusing! Hopefully this will help anyone else led here by search engine. And thanks again for the info neznein.