masc instr sg of yebhuyya (adj); nt instr sg of yebhuyya (adj)
Analysis. yebhuyya is an adjective meaning "whichever is greater/more"; yebhuyyena is its instrumental singular form used as an indeclinable adverb. ye- (relative pronoun "which") + bhuyya (comparative superlative form of bahu "much, many") + instrumental ending -ena. The instrumental case here functions adverbially to mark the manner or standard by which something is reckoned: "by the greater (part)", hence "mostly".
Etymology. yebhuyya compounds ye- (Pali relative stem, Sanskrit ya-, cognate with Greek hos and Latin qui) with bhuyya, the comparative/superlative of bahu "much, many" (Sanskrit bahú-, cognate with English "big" in the sense of magnitude, though the surface forms diverged). The adverbial instrumental -ena derives from Proto-Indo-European instrumental case marker. The sense develops naturally: "by the greater portion" > "mostly".
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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