Gladly

wiktionary

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From Middle English gladly, gladliche, from Old English glædlīċe(“gladly”); equivalent to glad +‎ -ly. Compare Danish glædelig(“joyful”), Icelandic gleðilegur(“delightful”). More at glad, -ly.

etymonline

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gladly (adv.)

Old English glædlice "joyfully, kindly, willingly" (also "bright, shining; pleasant, agreeable"); see glad (adj.) + -ly (2).