neuter nominative/accusative singular, or adverbial form; literally 'in the past'
Analysis. bhūta (past participle of bhavati 'was, existed') + pubba (before, formerly); together 'what was before', used as an adverbial phrase introducing narrative.
Etymology. bhūta from √bhū (to be, become; cognates: English be, Greek physis 'nature'); pubba from Proto-Indo-European *per-, *pṛ- (forward, across; cognates: English fare, further, foremost); the pair functions like English 'once upon a time' or German 'Es war einmal'.
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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