Etymology
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forswear (v.)
Old English forswerian "swear falsely" (intransitive), also "abandon or renounce on oath" (transitive), from for- "completely" + swerian "to swear" (see swear (v.)). Related: Forswore; forsworn; forswearing.
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forsworn (adj.)
from Old English forsworen, "perjured," past participle of forswerian "to swear falsely" (see forswear).
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abjure (v.)
Origin and meaning of abjure

early 15c., abjuren, "renounce on oath, repudiate, forswear," originally especially "renounce or recant (a heresy) on oath," from Old French abjurer and directly from Latin abiurare "deny on oath," from ab "off, away from" (see ab-) + iurare "to swear," from ius (genitive iuris) "law" (see jurist). Related: Abjured; abjuring.

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