*aiþastabaz

From *aiþaz + *stabaz, with the second constituent in the specialized sense ‘word, clause, formula’; thus literally ‘oath-wording’ rather than ‘oath-staff’ (Carr 1939: 46; Love et al. 2020: s.v. eiðstafr; Orel 2003: 10). The compound is continued by Old Norse eiðstafr, while Old English āþstæf, Old Saxon ēdstaf, and Middle High German eitstap show metonymic generalization from the formula to the oath itself (Orel 2003: 10).

The first constituent*aiþaz continues Celto-Germanic *oito-s (‘oath’), traditionally derived from Proto-Indo-European *h₁óy-to-s, from root *h₁ey-, though both the PIE derivation and the possibility of early Celtic borrowing remain uncertain. Cognate with Old Irish óeth and perhaps Ancient Greek οἶτος (oîtos) and Old Phrygian *oito- (Mallory & Adams 1997: 408–409; Orel 2003: 10). The second consituent, *stabaz, ultimately belongs to Proto-Indo-European root *stebʰ-, with cognates including Sanskrit स्तभ्नाति (stabhnāti), Lithuanian stãbas, and Middle Irish sab (Orel 2003: 368).