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