accusative singular, adverbial; contraction of etaṁ + atthaṁ
Analysis. etaṁ (demonstrative accusative 'this') + atthaṁ (accusative of attha 'meaning, purpose, reason') — 'this-purpose'; used adverbially to mean 'for this reason' or 'to this end'
Etymology. attha derives from Sanskrit artha- 'meaning, purpose, object', from Indo-European *ar- 'fit, join' (English 'art' as skill, Latin ars); the dative etassatthāya is also common.
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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