Eighth

wiktionary

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From Middle English eiȝtthe, from Old English eahtoþa, from Proto-Germanic *ahtudô.

etymonline

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eighth (adj., n.)

"next in order after the seventh; an ordinal numeral; being one of eight equal parts into which a whole is regarded as divided;" late 14c., eighthe, contracted from Old English eahtoða, from Proto-Germanic *ahtudon (source also of Old High German ahtoda, Old Frisian achta, German achte, Gothic ahtuda);see eight + -th (1).