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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 (e.g. Dutch blozen "to blush") and Scandinavian (e.g. 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.
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.
A sudden and brief redness of the face and neck due to emotion; flush.