Old English wincian ‘close the eyes’, of Germanic origin; related to German winken ‘to wave’, also to wince.
The meaning “close an eye as a hint or signal” is first recorded c. 1100; that of “close one’s eyes (to fault or irregularity)” first attested late 15c. Related: Winked; winking. “a quick shutting and opening of the eyes,” c. 1300, from wink (v.); meaning “very brief moment of time” is attested from 1580s
A wink is a facial expression made by briefly closing one eye. A wink is an informal mode of non-verbal communication usually signaling shared hidden knowledge or intent. However, it is ambiguous by itself and highly dependent upon additional context, without which a wink could become misinterpreted or even nonsensical.