Wink/wink of sleep
Wink of sleep is usually expressed in the negative, e.g. could or did not sleep a wink, and this usage dates from the 14th century, where a wink meant a closing of the eyes for a short sleep or nap. Since this time, wink has meant a quick closing and opening of the eyes, the same as a blink, which dates from the early 1600s. The meaning of wink as in to give a significant, knowing or conspiratorial movement of the eyelid dates only from the early 19th century. See also Tip someone the wink.