h₃eyt-
“to swear an oath”oath, swear
PIE root meaning to swear an oath. Source of English "oath" and Germanic words for solemn pledges.
Discussion
*h₃eyt- is the Proto-Indo-European root meaning "to swear an oath, to go" (with the oath sense possibly derived from a notion of "going" toward a solemn commitment). The root is primarily attested in the Germanic branch for its oath-related meaning.
Old English āþ "oath" descends from Proto-Germanic *aiþaz, from PIE *h₃eyto-. Modern English "oath" preserves this with regular sound changes. The word carried immense legal and religious weight in Germanic society — oath-breaking was among the gravest offences in early medieval law codes.
Old High German eid, Old Norse eiðr, and Gothic aiþs all continue the same Proto-Germanic form. The Irish óeth "oath" is sometimes cited as a Celtic cognate, though this may be a Germanic loanword.
The connection to PIE *h₃ey- "to go" (whence Latin īre "to go") is debated. If valid, the semantic development would parallel other cultures where swearing an oath involves ritual movement — stepping forward, walking between sacrificial halves, or processing to a sacred site. Some scholars instead connect the root to *h₁ey- "to bind," which would give a more straightforward semantic path to "oath" as a binding declaration.
The root's limited branch distribution (primarily Germanic and possibly Celtic) makes its exact PIE form less certain than widely attested roots.
Notes
Source of Germanic *aiþaz > English "oath". Celtic *oito-.
Related Roots
English Words from *h₃eyt-
These modern English words descend from this root. Each page traces the full journey from PIE to present-day English.