grammatical number - Plural nouns in nominal compounds

I wonder whether there are rules or guidelines regarding plural nouns in nominal compounds. For example a compound university students list. If there are many lists and many universities is it grammatically correct to say universities students lists? Must all elements be in the plural form or can some be left in singular, even though the meaning is plural? I've seen an expression universities student lists; is it correct?

Answer

There is a cross-linguistic principle that words incorporated into compounds tend to lose any inflections (I remember an article in Language in the 80's - probably, from the index, one of the articles in Vol 62 No 1, but I haven't a copy to hand).

So in English, the norm is that nouns incorporated into compounds do not take a plural ending. Where they do, this is usually because the singular form would be ambiguous, often because there is a homophonous adjective. An example I recall is "solid modelling" - the company I worked for in the 80's used this phrase (in the UK, hence the spelling of "modelling"), but other vendors preferred "solids modeling", presumably because they thought that "solid modelling" might be a solid kind of modelling, as opposed to the modelling of solids.