whiten (v.)youdaoicibaDictYouDict[whiten 词源字典]
c. 1300, "to make white," from white (adj.) + -en (1). Intransitive sense "become white" is from 1630s. Earlier verb was simply white (late Old English). Related: Whitened; whitening; whitener.[whiten etymology, whiten origin, 英语词源]