English. Etymology. There are many meanings of the word 'tight' and, unsurprisingly, there are several theories going the rounds as to the origin of ' sleep tight'. One is that the phrase dates from the days when mattresses were supported by ropes which needed to be pulled tight to provide a well-sprung bed. What's the meaning and origin of the phrase 'Sleep tight'?. Learn the easiest way to fold a top sheet to have perfect hospital corners. HGTV. com shows you how.