Sol (n.)youdaoicibaDictYouDict[Sol 词源字典]
"the sun personified," mid-15c. (also in Old English), from Latin sol "the sun, sunlight," from PIE *s(e)wol-, variant of root *saewel- "the sun" (cognates: Sanskrit suryah, Avestan hvar "sun, light, heavens;" Greek helios; Lithuanian saule; Old Church Slavonic slunice; Gothic sauil, Old English sol "sun," swegl "sky, heavens, the sun;" Welsh haul, Old Cornish heuul, Breton heol "sun;" Old Irish suil "eye").

The PIE element -*el- in the root originally was a suffix and had an alternative form -*en-, yielding *s(u)wen-, source of English sun (n.). French soleil (10c.) is from Vulgar Latin *soliculus, diminutive of sol; in Vulgar Latin diminutives had the full meaning of their principal words.[Sol etymology, Sol origin, 英语词源]