From an old (unattested) adjective *dailus, which yielded two parallel forms, a yo-stem adjective (> standard daiļš) and an o-stem adjective (> dialectal dails), from Proto-Baltic *day- with an extra suffix -l, from the o-grade form of Proto-Indo-European *dey-, *doy- (“to shine brightly, to glitter, to sparkle”). There was some influence in the meaning of this word from a homophonous Proto-Indo-European stem *dey- (“to swing, to sway, to swirl; to rush”), from which the uses of daiļš to mean “quick, industrious, diligent, skilled” (mostly in folk songs or tales). Cognates include Lithuanian dailùs (“pretty, beautiful, lovely, tasteful”), Sanskrit दीद्यति (didyati, “to shine, to glitter, to sparkle”), Ancient Greek δέατο (déato, “was visible, appeared, seemed”), Irish river name Daol, from Proto-Celtic *doilā (“shining, bright”).