*bi

From Proto-Indo-European *h₁epí with accent on the second syllable (compare Ancient Greek ἐπί (epí) (epí, ‘on, upon; at, near’)) from *h₁épi (‘on, at, near’), locative case of *h₁éps, from root *h₁ép- (‘grab, snatch, get’). The Proto-Germanic -b- reflects voicing of earlier -p- by Verner’s Law, which presupposes a preform with accent on the second syllable. This seems more likely than an origin from a zero-grade form, *h₁pi, since the phonology is simpler: 1. Accent moved to second syllable. *h₁épi > *h₁epí 2. Loss of laryngeal *h₁epí > *epí 3. Grimm’s Law *epí >*efí 4. Verner’s Law *efí > *ebí 5. Loss of the unaccented initial syllable *ebí > *bi. (Ringe 2017) also notes this as the etymon for the ib- in Gothic 𐌹𐌱𐌳𐌰𐌻𐌾𐌰 (ibdalja, ‘mountainside, hillside, descent’) and 𐌹𐌱𐌿𐌺𐍃 (ibuks, ‘backward, back’), clearly showing the initial vowel intact, likely having remained due to its initial placement in the compounds. A further argument against the zero-grade formation is *fanē (‘from’) < *h₂pó: even with the accent on the second syllable, it clearly shows no Verner’s Law effect in Proto-Germanic, showing that loss of initial laryngeal likely occurred before Verner’s Law could take effect.