The story
- Proto-Germanic*gladaz
- Proto-West Germanic*glad
- Old Englishglæd
- Proto-Indo-European*leyg-
- Proto-Germanic*līką
- Old Englishglædlīċe
- Middle Englishgladly
- English todaygladly
Inherited from Middle English gladly (“joyousuly, voluntarily, easily”), from Old English glædlīċe (“gladly, pleasantly, kindly”), from glæd (“glad, bright”) + -līċe. Compare Danish glædelig (“joyful”), Icelandic gleðilegur (“delightful”). More at glad, -ly.
Etymology from Wiktionary, CC BY-SA 4.0.