OK, I'll have a guess. If you have nine girls named April, the ninth of them will be Den nionde April. If you want to speak about nine instances of the month April, you could possibly say Den nionde aprilmånaden or something like that but I think you ought to rephrase this completely both in Swedish and in English.
Promethea.b makes a good point and might be right. But I couldn't stop thinking if it may be that months or at least April could be an -en word. As if I wanted to tell a story starting with: One April... I was walking around... when... Or if it is thought differently when starting a sentence in that way.
Besides, this same question took me to look closer to the construction of the sentence and it reminds me of the form: Den/Det + adjective(-a) + definite noun. I was wondering if I might be confusing adverbs with adjectives... or something else... and if I could suppose that months are not 'defined'. Thinking on the idea Arnauti gave about months being historically written in the Latin genitive. Thank you! =)
I understand what you say... But my question was taking a different way... Although månade is an en-word I was wondering if when you talk about particular months you would talk about them as en or ett words... And I mentioned the idea of the construction of the sentence... Specifically on the use of nionde because as far as I understood it was being used as an adjective here... [Edit... But I see your point now... With the of it takes another form and I did not undetstand that... Thank you]. But in the case the month would be described..., Could it be defined... I am taking the idea that it is not and that it is just how we have to use them. Tho it could be interesting to know why if it is the case and if it is related to Arnauti's comment up here... That months were writen in the Latin genitive... Anyway, as you say this last may have not been a very relevant question... Althought It would be nice to know the first one... But again perhaps we'll get that later on the course and I should wait to see... =)...
I can totally see why it's counter intuitive. On the other hand we do have other prepositionless expressions, like en kopp kaffe 'a cup of coffee' too. For months, they were historically written in the (Latin) genitive e.g. 1 Junii for 'June 1st' so that may be one reason.