:Huh, I didn't even know that there was a difference. Sadly, I can't supply any references (so I can't add anything to the article itself), but as someone from the US who used to be an avid game player, including having worked in a retail game store for about 5 years, I always thought that the singular form is "die". However, its very common in English language evolution for singular and plural forms to converge into a single, standardized form (in general, there's a general long term tendency to eliminate irregular forms in most languages), so it may be that in the UK the distinction disappeared, and perhaps is also disappearing in the US. I'm not quite sure where to go to, other than to other dictionaries, to figure out what to put in the article, though.