Why is the ninth month called September?
Old English hwit, from Proto-Germanic *khwitaz (cf. Old Saxon and Old Frisian hwit, Old Norse hvitr, Dutch wit, Old High German hwiz, German weiß, Gothic hveits), from PIE *kwintos/*kwindos "bright" (cf. Sanskrit svetah "white;" Old Church Slavonic sviteti "to shine," svetu "light;" Lithuanian sviesti "to shine," svaityti "to brighten").
As a surname, originally with reference to fair hair or complexion, it is one of the oldest in English, being well-established before the Conquest. Meaning "morally pure" was in Old English. Association with royalist causes is late 18c. Slang sense of "honorable, fair" is 1877, American English. The racial sense (adj.) of "of those races (chiefly European or of European extraction) characterized by light complexion" is first recorded c.1600. The noun in this sense ("white man, person of a race distinguished by light complexion") is from 1670s. White supremacy attested from 1902; white flight is from 1967.
White heat "state of intense or extreme emotion" first recorded 1839. White lie is attested from 1741. White Christmas is attested from 1857. White House at the U.S. presidential residence is recorded from 1811. White water "river rapids" is recorded from 1580s. White Russian "language of Byelorussia" is recorded from 1850; the mixed drink is from c.1978. White-collar as an adjective is from 1921; white-collar crime attested by 1964 (there is a white-collar criminaloids from 1934). Astronomical white dwarf is from 1924.
a symbol of purity (2 Chr. 5:12; Ps. 51:7; Isa. 1:18; Rev. 3:18; 7:14). Our Lord, at his transfiguration, appeared in raiment "white as the light" (Matt. 17:2, etc.).