Where does “lessom” come from?

lessom (Old Irish) comes from Old Irish lés, from Proto-Celtic *ḷsso-s, from Proto-Indo-European *pl̥t-to-.

Ancestry of “lessom”, step by step

StepLanguageWordMeaning
1Old Irishléslight, radiance; daylight; illumination
2Proto-Celtic*ḷsso-s—
3Proto-Indo-European*pl̥t-to-—
Every word from Proto-Indo-European *pl̥t-to- →Every word from Proto-Celtic *ḷsso-s →Every word from Old Irish lés →