Mighty

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Old English mihtig (see might2, -y1).

wiktionary

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From Middle English mighty, mightie, mighti, myghty, miȝty, maȝty, from Old English mihtiġ, mehtiġ, meahtiġ, mæhtiġ(“mighty”), from Proto-West Germanic *mahtīg(“mighty”), from Proto-Germanic *mahtīgaz(“mighty”), equivalent to might +‎ -y.

Cognate with Scots michty, mychty, Saterland Frisian machtich, Dutch machtig, German Low German machtig, German mächtig, Swedish mäktig.

etymonline

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mighty (adj.)

"possessed of or endowed with might; having much ability, strength, or power," Old English mihtig, earlier mæhtig, from Proto-Germanic *mahtiga- (source also of Old Frisian mechtig, Old Saxon mahtig, Dutch machtig, German mächtig), from the source of might (n.). As an adverb, "very, exceedingly, greatly," it is attested from c. 1300, though such use now is considered colloquial.