Sibyl is a proper noun, and sybil is an alternate spelling. With my dictionary, sybil is flagged as misspelled, so it should actually be added to the Personal Dictionary: in a Write window, Options/Check Spelling, Add Word.

Within the community that talks about "sybil attacks", sibyl is an unusual spelling and people who read it are likely to subconsciously view the writer as ignorant and an outsider.

Maybe it is a correct spelling when you are talking about greco roman literature, but it is not a correct spelling in the community where "sybil" is a term of the art.

You can't expect dictionaries to cater to specialized communities, and besides, nobody is forced to use 'sibyl' if 'sybil' is preferred.

Anyone who thinks 'sibyl' indicates ignorance of the writer needs to consult a dictionary before making judgments.

A dictionary running on my computer should cater to me, and if it does not I should be able to edit it.

And someone who writes "sibyl" for sybil may not be indicating ignorance of classic Greek literature, but he is indicating ignorance of the art and theory of graph theory and computer security.

Unless you want to go the route of creating your own dictionary, I would suggest your stuck with ancient greek oracles called sibyls being considered correct spelling.

I could also argue that Americans are all ignorant because they do not know how to write the date and can not spell gaol, while my preference for date is accommodated by my operating system although I am often still mystified about post on this form that tell me everything worked fine until 10/1 Do they mean January or October. I really have to guess. my dictionary appears to think Gaol is spelled Jail. I can add Gaol, but I can not remove Jail because the community I live in is fast adopting those same US centric spellings. So I guess you need to look at accepting that dictionaries contain a lot of words that you may never use that will be considered "correct". Not everything can be fixed with auto correct and a dictionary.

The Thunderbird dictionary is on my computer - somewhere.

If I simply knew where it was, I could change it.