(adverb) - (1) Though it has been plausibly suggested that the comparison has reference to the rapid passage of the welkin, or cloud, through the heavens, the last word of the expression is probably a contraction of winking, meaning the time taken to wink the eye. We have, moreover, almost an exact parallel in the French clin d'oeil, and our own expression, in a wink, an abbreviation of twinkle, the opening or shutting of the eye, and again in German Augenblick, a moment.
--A. Wallace's Popular Sayings Dissected, 1895
(2) Like winking, with vigour or persistency; "like anything." So, easy as winking.
--Sir James Murray's New English Dictionary, 1928
(3) Both my legs began to bend like winkin.
--Thomas Hood's Sailor's Apology for Bow-Legs, 1827