[susan53]

Games. I've searched the internet and gone through my favourite book on language - Steven Pinker's The Language Instinct - and I still can't find the answer. Pinker says (p46 of the Penguin version) :

"compounds can be formed out of irregular plurals but not regular plurals. For example, a house infested by mice can be described as mice-infested but it sounds awkward to describe a house infested by rats as rats-infested. We say that it is rat-infested even though by definition one rat does not make an infestation".

But that is contradicted by the computers textbook or the games room. And there are plenty of examples of nouns with irregular plurals which still use the singular in compounds :toothbrush, footpath, man-eater, woman hater, child molester

All my other grammar books are in my office. I'll check this afternoon and come back if I find out anything more.