Seventy

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Old English hundseofontig, from hund- (of uncertain origin) + seofon ‘seven’ + -tig (see -ty2).

wiktionary

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From Middle English seventy, sevynty, from Old English hundseofontiġ, from Proto-Germanic *sebuntēhundą(“seventy”), equivalent to seven +‎ -ty. Cognate with Scots sevinty(“seventy”), Saterland Frisian soogentich(“seventy”), West Frisian santich(“seventy”), Dutch zeventig(“seventy”), German Low German söventig(“seventy”), German siebzig(“seventy”), Swedish sjuttio(“seventy”), Norwegian sytti(“seventy”), Icelandic sjötíu(“seventy”).

etymonline

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seventy (adj., n.)

"1 more than sixty-nine; the number which is one more than sixty-nine; a symbol representing this number;" Old English (hund)seofontig, from seofon (see seven) + -tig (see -ty (1)). Similar formation in Old Frisian soventich, Middle Dutch seventich, Old Norse sjau tiger.