In the Straight Dope Mailbag,
http://www.straightdope.com/mailbag/msleepti.html
you state more or less unequivocally that the phrase “Sleep tight…” has its origin with early rope-string beds. While this has a nice ring to it (like the bogus “brass monkey” sailing explanation) I think you at least need to give mention to the somewhat more scholarly opinions that disagree with this explanation.
From AskOxford.com:
"It seems that tight in this expression is the equivalent of the only surviving use of the adverb tightly meaning ‘soundly, properly, well, effectively’. The full Oxford English Dictionary labels the adverb ‘now dialectal’ and the adjective ‘colloquial’. The phrase Good night, sleep tight is a conventional (rhyming) formula used when parting for the night or at bedtime. "
Similarly, from Wordorigins.org:
"Sleep Tight
I heard one explanation for the origin of this term while visiting Shakespeare’s birthplace in Stratford-on-Avon. The tour guide (tour guides are wonderful sources of apocryphal information) told us that the sleep tight derived from the fact that Elizabethan beds had a foundation consisting of a rope net. When the bed began to sag, one would tighten the net. Well, such beds do exist (there is one in the Bard’s birthplace), but they are not the origin of the term.
One of the archaic senses of tight means soundly or roundly. It dates to the late 18th century and survives today only in the phrase sleep tight. The usage postdates Shakespeare and Elizabethan England by a century or so.
I have also heard various explanations about how children would be bound to the bed or bedclothes would be secured, giving rise to the phrase. All of these would appear to be false. The children’s rhyme beginning ‘Good night, sleep tight…’ dates only to the late 19th century."
I admit to a pet peeve regarding the many false word origins that circulate on the Internet. I rely on Straight Dope to deliver a clear and factual response.
Thanks,
Fred Strathmann