Lightly

wiktionary

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From Middle English lyghtly, liȝtliche, lihtliche, from Old English lēohtlīċe, equivalent to light +‎ -ly.

etymonline

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lightly (adv.)

Old English leohtlice "so as not to be heavy" (of material things, but also of sleep, blows, etc.), from light (adj.1) + -ly (2). Similar formation in Old Frisian lichtelik, Old High German lihtlihho, German leichtlich, Old Norse lettlega (see light (adj.1)). Meaning "frivolously, indifferently" is from early 13c. (compare Old English leohtmodnes "frivolity").