Sworn

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Old English swerian of Germanic origin; related to Dutch zweren, German schwören, also to answer.

wiktionary

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From Middle English sworen, isworen, from Old English sworen, ġesworen, from Proto-West Germanic *swaran, *giswaran, from Proto-Germanic *swaranaz, past participle of Proto-Germanic *swarjaną(“to swear”), equivalent to swear +‎ -en.

etymonline

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sworn

past participle of swear; sworn enemies, those who have taken a vow of mutual hatred, is from c. 1600.