Should read A Cappella ?
I have two different genres, A Cappella and Acapella and can’t merge them.
Good spot!
Neither appear in the Genre mapping tool. The only Genre that crops up when I search is Jazz a capella
Also the search box in the Genre tool is very slow on my iPad. I think Ben may have optimised the general search text box. This might need a look too.
The issue is not the spelling, which is apparently commonplace in the US; the issue I flagged for support is that @andybob is not able to do the mapping.
Understood about support. But as per the OP “Acappella” is an incorrect spelling of a centuries-old term, as the website you linked to points out. It’s correct (but still spelled two different ways!) in the accompanying text in the screenshot above.
I guess this mess comes from Rovi? 
@andybob — Thanks for the report! Can you confirm what your “genre” settings are under the “library” tab?
-Eric
Hi Eric, thanks for helping with this.
My Library/Import Settings/Genre Settings:
My Genre mappings tool:
Genres sorted by name (Vale Chris …):
I’ve inherited far too many Genres to be useful and am trying to prune 5 a day.
I have made A Cappella a top level genre and removed all albums from Acappella. Might that be why neither appears in the mapping tool ?
So, the genre “A Cappella” comes from your file tags, and doesn’t appear on the left side of the mapping list at all?
The second screenshot seems to be showing that, but I’m just confirming that’s the start of the list.
Hi Mike,
Yes, that’s right.
Mike has helped sort this out. My genre “A Cappella” is just a Roon edit, not a file tag. That is why it doesn’t appear in the Merge Genre’s tool.
Also we can’t merge a Roon Genre to our own file tag Genres. I don’t know enough about Genres in Roon to know whether that would break things.
So I shall make everything unaccompanied vocal map to Acappella and vacate my edit Genre. I like that language usage changes and, as Joel pointed out, it has now become a term, albeit demotic.