locative singular of kathāvatthu (noun, neuter)
Analysis. kathā (speech, discourse) + vatthu (subject, matter) = "subject of speech"; the locative ending -smiṁ places it in the location or context specified.
Etymology. kathā from √kath- "speak" (related to Sanskrit kathayati); vatthu from √vat- "turn, roll", hence "that which turns or goes" — a subject that the discussion revolves around. English "what" ultimately shares the same Indo-European root as kathā.
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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