on the blink

1580s, perhaps from Middle Dutch blinken "to glitter," of uncertain origin, possibly, with German blinken "to gleam, sparkle, twinkle," from a nasalized form of base found in Old English blican "to shine, glitter" (see bleach (v.)).

Middle English had blynke (c.1300) in the sense "a brief gleam or spark," perhaps a variant of blench "to move suddenly or sharply; to raise one's eyelids" (c.1200), perhaps from the rare Old English blencan "deceive." Related: Blinked; blinking. The last, as a euphemism for a stronger word, is attested by 1914.