noun
soft light; faint sunlight
Refers to weak, gentle sunlight, often when the sun is partially obscured by clouds or haze. Common in literary or descriptive contexts.
雲の切れ間から薄日が差し込んだ。
Soft sunlight streamed through a break in the clouds.
薄日の下で庭の花がほのかに輝いていた。
The garden flowers glowed faintly under the soft light.
Compound of 薄 (usu-, 'thin, weak') + 日 (hi, 'sun, sunlight'), with rendaku voicing of hi to bi. The meaning is transparently 'weak sunlight'.