*ēbanþs

Uncertain. Following Hamp’s analysis (Lloyd & Springer 1988-2014), adopted by (Kroonen 2013), *ēbanþs may continue an earlier acrostatic formation based on an innovative nt-stem, *h₁éh₁pt-ont-s ~ *h₁h̥₁pt-n̥t-ós, with strong cases yielding West Proto-Germanic *ēbanþ- and weak cases ultimately reflected in North Proto-Germanic *aft-/apt-. In this account, the West Proto-Germanic forms reflect a dissimilated oblique formation *h₁eh₁pt-ont- > *h₁eh₁p-ont-, in which the first dental of *-pt-ont-was lost before regular Proto-Germanic sound changes produced *ēbanþ- ~ *ēbund-. The North Proto-Germanic forms are then explained from the zero-grade *h₁h̥₁pt-n̥t-ós, with vocalization of the syllabic laryngeal to *a and development of *pt to *ft by Grimm’s Law; the resulting *aft-/apt- stem was generalized in North Proto-Germanic. This explanation is attractive because it elegantly accounts for the otherwise difficult split between West Proto-Germanic *ēb-/āb- and North Proto-Germanic *aft-/apt-.

(Beekes 1996a:231–32: 231–32) instead treats the word as a probable ancient European loanword, emphasizing that the suffixal type in *-ont-is rare in Proto-Germanic and may point to borrowing rather than inheritance. His strongest argument is the distribution of the vowels: the long vowel occurs before single *-p-in the open-syllable type, while the short vowel occurs before *-pt-, a pattern which he compares with other suspected substrate loanwords and regards as evidence that the alternation originated in a substratum rather than in PIE ablaut, as vowel shifts dependent on syllable weight are highly unusual for primary Indo-European nominal derivations but are typical of loanwords adapted from languages with different prosodic systems. He reconstructs a European substrate form, approximately *apt-an(t)- ~ *āp-an(t)- (‘evening’), with the foreign vowel later adapted differently in Proto-Germanic. The root *h₁eh₁pt, in any case, cannot be of Proto-Indo-European origin (Šorgo 2020).