adverb (sandhi form with eva); instrumental singular neuter of khippa used adverbially
Analysis. khippaṃ + eva: khippaṃ (instrumental neuter singular of khippa, 'quickly') + eva ('indeed, very'), intensifying the adverbial sense to 'very quickly, with utmost speed'.
Etymology. Khippa derives from √khip (to throw, cast), cognate with Sanskrit kṣip-. The instrumental neuter singular khippaṃ ('in a quick manner') is adverbially idiomatized; eva ('indeed, very') intensifies it, a common Pali construction. The root imagery is 'thrown' — swift as something hurled — which grounds the sense of rapidity.
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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