OATH (n.) Old English að “oath, judicial swearing, solemn appeal to deity in wit

OATH (n.)

Old English að “oath, judicial swearing, solemn appeal to deity in witness of truth or a promise,” from Proto-Germanic *aithaz (source also of Old Norse eiðr, Swedish ed, Old Saxon, Old Frisian eth, Middle Dutch eet, Dutch eed, German eid, Gothic aiþs “oath”), from PIE *oi-to- “an oath” (source also of Old Irish oeth “oath”). Common to Celtic and Germanic, possibly a loan-word from one to the other, but the history is obscure.