"Pentecost," late Old English Hwita Sunnandæg "white Sunday" (see white (adj.)); possibly so called from the white baptismal robes worn by newly baptized Christians on this day. Related: Whitsuntide.
Entries linking to Whitsunday
Old English hwit "bright, radiant; clear, fair," also as a noun (see separate entry), from Proto-Germanic *hweit- (source also of Old Saxon and Old Frisian hwit, Old Norse hvitr, Dutch wit, Old High German hwiz, German weiß, Gothic hveits), from PIE *kweid-o-, suffixed form of root *kweit- "white; to shine" (source also of Sanskrit svetah "white;" Old Church Slavonic sviteti "to shine," svetu "light;" Lithuanian šviesti "to shine," švaityti "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; in Middle English it meant "gracious, friendly, favorable." The racial sense "of those races (chiefly European or of European extraction) characterized by light complexion" is recorded from c. 1600; meaning "characteristic of or pertaining to white people" is from 1852, American English. White supremacy attested from 1868, American English [John H. Van Evrie, M.D., "White Supremacy and Negro Subordination," New York, 1868]; white flight is from 1966, American English.
White way "brightly illuminated street in a big city" is from 1908. White flag of truce or surrender is from c. 1600. White lie is attested from 1741. White Christmas is attested from 1847. White House as the name of 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. Astronomical white dwarf is from 1924. White witch, one who used the power for good, is from 1620s.