ὀμνύω ; to swear, i.e. take (or declare on) oathDerivation: a prolonged form of a primary, but obsolete ὄμω, for which another prolonged form ὀμόω is used in certain tenses;KJV Usage: swear.
Thayer:1) to swear 2) to affirm, promise, threaten, with an oath 3) in swearing to call a person or thing as witness, to invoke, swear by
ὀμνύω omnuō om-noo'-o A prolonged form of a primary but obsolete word, ὄμω omō , for which another prolonged form ( ὀμόω omoō om-o'-o ) is used in certain tenses. To swear, that is, take (or declare on) oathKJV Usage: swear.