indeclinable particle
Etymology. From yad- (relative pronoun, 'which, what') + -thā (ablative/locative suffix forming adverbs of manner). Cognate with Sanskrit yathā; the root yad- is related to Latin qui, quid and English who, what (all from Proto-Indo-European *kwo-). The suffix -thā appears also in athā 'then' and kathaṁ 'how' and derives from an old ablative or locative case ending.
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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