Where does “fullheartedly” come from?

fullheartedly (English) comes from English fullhearted, from English full, from Middle English fúl, from Old English full, from Proto-West Germanic full, from Proto-Germanic fullaz, from Proto-Indo-European pl̥h₁nós, from Proto-Indo-European pleh₁- — to fill.

Ancestry of “fullheartedly”, step by step

fullheartedly traces back through two separate lines of ancestry.

via English fullhearted

StepLanguageWordMeaning
1EnglishfullheartedWholehearted; Full of courage or confidence;...
2EnglishfullContaining the maximum possible amount that can...
3Middle Englishfúlvery; much; to a great extent
4Old Englishfullfull, filled, complete, entire; a beaker; a cup,...
5Proto-West Germanicfullfull
6Proto-Germanicfullazfull; the whole, the entire
7Proto-Indo-Europeanpl̥h₁nósfull
8Proto-Indo-Europeanpleh₁-to fill

via English ly

StepLanguageWordMeaning
1EnglishlyAbbreviation of light-year
2VietnameselyAlternative spelling of li
Every word from Proto-Indo-European pleh₁-