light (adj.1)youdaoicibaDictYouDict[light 词源字典]
"not heavy," from Old English leoht "not heavy, light in weight; easy, trifling; quick, agile," from Proto-Germanic *lingkhtaz (cognates: Old Norse lettr, Swedish lätt, Old Frisian, Middle Dutch licht, German leicht, Gothic leihts), from PIE root *legwh- "not heavy, having little weight" (cognates: Latin levis "light," Old Irish lu "small;" see lever).

The notion in make light of (1520s) is of "unimportance." Alternative spelling lite, the darling of advertisers, is first recorded 1962. The adverb is Old English leohte, from the adjective. Light-skirts "woman of easy virtue" is attested from 1590s. To make light of is from 1520s.[light etymology, light origin, 英语词源]