A person who studies, promotes, or is devoted to Celtic cultures, languages, history, and traditions.
From Celt plus the suffix -ist (meaning one who practices or specializes). This synonym for Celticist emerged in the 19th century as scholarly terminology became standardized in academic circles.
Having both 'Celticist' and 'Celtist' as options is one of those funny English quirks where the language gives you multiple ways to say the same thing, and nobody's quite sure which one will win out in the long term.
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