Blindly

wiktionary

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From Middle English blindly, blyndly, from Old English blindlīċe(“in a blind manner; blindly; rashly”), equivalent to blind +‎ -ly. Cognate with Swedish blindligt(“blindly”), Icelandic blindlega(“blindly”). Compare also West Frisian blindich(“blindly”), Dutch blindelings(“blindly”), German blindlings(“blindly”).

etymonline

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blindly (adv.)

"in a blind manner; without sight; without reasoning," Old English blindlice; see blind (adj.) + -ly (2).