"I have important visitors."
Translation:Jeg har viktig besøk.
so how do you know the meaning is plural if both words (viktig,besøk) refer to singular objects?
The same reason 'group' is a singular word in English, yet it doesn't describe a single person :)
Because that's not a word in Norwegian.
You'd use either the singular "besøk" (which can be plural in meaning), or "gjester".
I said "Jeg har viktige besøkende" and it okayed it. Does that make sense as well? Or is it just best to say "Jeg har viktig besøk"?
Is "besoker" not used as a plural for "visitors" because it's a verb or is there some other rule or idiosyncrasy at work here?
Besøk is a neuter noun with no suffix for its plural indefinite form -- which usually applies to single-syllable neuter nouns, but also applies to some multisyllabic ones, too. (I realize this is 7 months later, but this answer could be useful to others.)
It's just not a word in Norwegian.
You need to use either "besøk", "gjester" or "besøkende" (in order of preference).