Hi,
I got surprised seeing Ørberg use the genitive plural form “arborum” (Fabellas Latinas, story no. 22 et passim). I expected a long o, but my favourite dictionary app agrees with Ørberg. However, I also checked https://latin.cactus2000.de/noun/shownoun_en.php?n=arbor&form=arbor, and it does give the form with a long o.
Why this confusion? And is Ørberg correct?
I notice that words like “labor” and “cantor” have a long o in the genitive plural. Are they somehow different? And why?
Munchped
You must know that -or doesn’t necessarily reflect the same origin and take in account that the nominative evolved separately from the other cases because of a different phonetic environment and analogy.
So you can have -or -ōris such as agent nouns (cantor, victor…) or other forms that merged with it (color), and also -or -oris that didn’t merge. You can also check various related forms such as tempus temporis, onus oneris that may cause even more confusion but also help you understand that situation.
I think I remember having read something about arbōris, but it’s a non standard form analogically formed from -or -ōris, and so you should disregard it in your lectures.