the idea of perjury: there is an implicit connection between the oath which is taken and the lie (the crooked words) which it supports. The idea, therefore, is the «addition» (epì) of an oath (hórkon) to a statement or a promise which one knows is false.
Benveniste demonstrates etymologically that perjury is structurally defined as the deliberate annexation of an oath to a known falsehood, tracing the compound epíorkos to its Hesiodic origins.
, Indo European Language and Society, 1973thesis