oath Look up oath at Dictionary.com
O.E. aš "oath, judicial swearing, solemn appeal to deity in witness of truth or a promise," from P.Gmc. *aithaz (cf. O.N. eišr, Swed. ed, O.Fris. eth, Du. eed, Ger. eid, Goth. aižs "oath"), from PIE *oi-to- "an oath" (cf. O.Ir. oeth "oath"). In ref. to careless invocations of divinity, from c.1175.