This is a very frequently used English expression which is used across many English speaking countries. If you would like to learn how to use this expression currently then keep reading!
The expression is used in order to denote that someone has slept well. Oftentimes someone will say “sleep tight” to someone before they go to bed in order to wish them a good sleep.
The expression was first used in1866 in the diaries entitled Through Some Eventful Years by Susan Bradford Eppes which read “”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.” However it was in the latter half of the 20th century that it was popularised when it was used in song lyrics by The Beatles. This was in the song Good Night in 1968, the lyrics of which read “Now it’s time to say good night, Good night. Sleep tight.”
The use of the word “tight” in the expression has a number of possible significances. Some argue that it relates to the bedcovers and the act of keeping them tight in order to avoid bedbugs entering the bed. On the other hand, others argue that the word “tight” is synonymous with “sound” and thus the expression simply means “sleep soundly.”
An example of the expression in use can be found in the commonplace expression “sleep tight, don’t let the bedbugs bite!” This is a phrase which is often uttered to children before going bed in order to urge them to remain in their beds and to wish them a good sleep.