The expression forty winks denotes a short sleep, especially during the day.
Here, the noun wink means a closing of the eyes for sleep. This sense has survived in the phrases not to sleep, or get, a wink, and not to get a wink of sleep, which both mean not to sleep at all. (This noun is from the verb to wink in its obsolete original sense of to close one’s eyes.)
The cardinal number forty has not only been used to denote the product of four and ten, but also as an indefinite term for a large number. There are frequent biblical references to forty days which mean no more than for a long time, and because of this frequency, the number forty came to have an almost sacrosanct quality, as the English clergyman and schoolmaster Ebenezer Cobham Brewer (1810-97) explained in Dictionary of Phrase and Fable (1st edition – London, 1870):
Forty. A superstitious number, arising from the Scripture use. Thus Moses was forty days in the mount; Elijah was forty days fed by ravens; the rain of the flood fell forty days, and another forty days expired before Noah opened the window of the ark; forty days was the period of embalming; Jonah gave Nineveh forty days to repent; Our Lord fasted forty days; he was seen forty days after his resurrection; etc.
The English poet and playwright William Shakespeare (1564-1616) used forty in this indefinite sense in The Tragedy of Coriolanus (Folio 1, 1623):
– Coriolanus. On faire ground, I could beat fortie of them.
– Menenius. I could my selfe take vp a Brace o’th’ best of
Likewise, on 19th January 1619, the poet and Church of England clergyman George Herbert (1593-1633) concluded a letter to his father-in-law, John Danvers, with these words:
I have forty businesses in my hands: your Courtesie will pardon the haste of
Your humblest Servant,
It is probably this sense, jocularly applied, that lies behind the expression forty winks, first recorded in The Art of invigorating and prolonging Life, by Food, Clothes, Air, Exercise, Wine, Sleep, &c. (London, 1821), by William Kitchiner (1775-1827), English optician, inventor of telescopes, amateur musician and cook:
Calling one day on a literary friend, we found him reclining on a Sofa—on expressing our concern to ﬁnd him indisposed, he said, “No, I was only hatching—I have been writing till I was quite tired—my paper must go to Press to day—so I was taking my usual restorative—A Nap— which if it only lasts ﬁve minutes, so refreshes my Mind—that my Pen goes to work again spontaneously.”
Is it not better Economy of Time, to go to sleep for half an hour,—than to go on noodling all day in a nerveless and semi-superannuated state—if not asleep, certainly not effectively Awake—for any purpose requiring the Energy of either the Body, or the Mind.
“A Forty Winks Nap,” in an horizontal posture, is the best preparative for any extraordinary exertion of either.
The use of quotation marks indicates that Kitchiner was probably quoting an existing phrase.
A variant appeared in Slang. A Dictionary of the Turf, the Ring, the Chase, the Pit, of Bon-ton, and the Varieties of Life (London, 1823), written by John Badcock under the pen name of Jon Bee:
Nine winks—a few minutes’ of sleep in the day, assuming to be for the space of time which would be occupied in winking the eye nine times. After he is roused, the doser prepares to take ‘nine corns more’ of tobacco, and ‘nine whiffs’ at his pipe.