(literary) Characterised by light; luminous; emitting or manifesting light; radiant.
This said, the smoky cloud was cleft and torn, / Which like a veil upon them stretched lay, // And up to open heav'n forthwith was borne, / And left the prince in view of lightsome day.
If any find it incredible that Ida be even outwardly so lightsome that she saw clearly in the night, let them answer this question.
adjective
Characterised by lightness of weight, not heavy; nimble, active.