Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English blencan "deceive, cheat," from Proto-Germanic *blenk- "to shine, dazzle, blind," from PIE root *bhel- (1) "to shine, flash, burn" (see bleach (v.)). Sense of "move suddenly, wince, dodge" is from c.1300. Related: Blenched; blenching.