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Sleep tight

Meaning

Sleep well.

Origin

This is a very well-used phrase in many parts of the English-speaking world. It's been common at bedtime for many years in the form of "good night, sleep tight, don't let the bedbugs bite", or similar.

There are several theories going the rounds as to the origin. One is that bedclothes were tied tightly to stop bedbugs biting. That's pure speculation and there seems to be no evidence whatsoever to support it. Another theory, this time a little more plausible, dates from the days when mattresses were supported by ropes which needed to be pulled tight to give a well-sprung bed. Again though, this is speculative.

The phrase "sleep tight" itself was well used in the late 20th century, but there could hardly have been better way of cementing any phrase into the popular consciousness than by Lennon and McCartney using it in the lyrics of a song at the height of Beatlemania. That's where it found itself, in Good Night on the White Album in 1968:

Now it's time to say good night,
Good night. Sleep tight.

The phrase actually isn't very old. The first citation found is from 1866. In her diary Through Some Eventful Years, Susan Bradford Eppes included:

"All is ready and we leave as soon as breakfast is over. Goodbye little Diary. ‘Sleep tight and wake bright,’ for I will need you when I return".

There aren't other known citations until L Frank Baum’s Rinkitink In Oz, 1916 and the OED has no others until 1933. This puts the phrase out of general circulation in the early 20th century, which tends to argue against the rope stringing origin as we might expect the common use of the phrase and the common use of rope-strung beds to coincide.

Susan Eppes' line, with its clear link between 'sleep tight' and 'sleep well', leads us to what is the most probable explanation for the phrase. The word tight, although not often used in this way now, means 'firm, sound, secure' (as in 'sit tight'). So, 'sleep tight' just means 'sleep soundly'.

The theories above, although they lack supporting evidence, are hard to finally disprove, but it is clear that there's a perfectly good explanation for this phrase without resorting to them.