means The visible light that travels from the sun and illuminates the Earth, whether streaming directly or filtered through cloud.

from A plain compound of two of English's oldest building blocks: "sun," from Old English "sunne" (a cousin of German "Sonne" and Latin "sol"), and "light," from Old English "lēoht," both tracing back to Proto-Germanic and ultimately Proto-Indo-European roots. The word does exactly what such honest compounds do — it bolts "sun" to "light" and trusts you to understand, a join old enough that no one remembers making it.