Sleep TightThe real origin of this common bedtime phrase.

From the show

History of Phrases

The popular story about tightening ropes on old beds is a myth. The phrase “sleep tight” actually comes from an older meaning of the word “tight,” which simply meant “soundly” or “properly.” So when someone tells you to sleep tight, they're just wishing you a sound sleep. This common expression likely survived because it rhymes so well with “good night,” not because of a forgotten piece of furniture.