That is very interesting. It seems that, assuming Fia is related, it would be a contraction of Dhuibh-Shith, with Dhuibh variously interpreted as black/dark/secret and Shith variously interpreted as fairy/magic/peace. That makes sense. Thanks! :)
"It's the job that is never started that takes the longest to finish." - J.R.R. Tolkien
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