blushyoudaoicibaDictYouDict[blush 词源字典]
blush: [OE] Modern English blush is a descendant of Old English blyscan ‘turn red, blush’, which was related to and perhaps derived from Old English blysa ‘firebrand, torch’. Similarities of form and meaning make it tempting to compare blaze, which meant ‘torch’ in Old English and came from a prehistoric Germanic *blasōn, but no connection has ever been established. Middle Dutch blosen ‘glow’ may be an intermediate form.
[blush etymology, blush origin, 英语词源]
blush (v.)youdaoicibaDictYouDict
mid-14c., bluschen, blischen, probably from Old English blyscan "blush, become red, glow" (glossing Latin rutilare), akin to blyse "torch," from Proto-Germanic *blisk- "to shine, burn," which also yielded words in Low German (Dutch blozen "to blush") and Scandinavian (Danish blusse "to blaze; to blush"); ultimately from PIE *bhel- (1) "to shine, flash, burn" (see bleach (v.)).

For vowel evolution, see bury. Earliest recorded senses were "to shine brightly; to look, stare." Sense of "turn red in the face" (with shame, modesty, etc.) is from c. 1400. Related: Blushed; blushing.
blush (n.)youdaoicibaDictYouDict
mid-14c., "a look, a glance" (sense preserved in at first blush), also "a gleam, a gleaming" (late 14c.), from blush (v.). As "a reddening of the face" from 1590s. Meaning "a rosy color" is 1590s.