(n.) a type of restraint device, typically used to prevent someone from harming themselves
Here’s a strange fact. Straitjackets were originally called strait-waistcoats.
The straitjacket as we know it today was invented in the mid eighteenth century, with a French upholsterer enigmatically known only as “Guilleret” popularly credited with its design. In the days long before violent psychiatric patients could be controlled with medication, a garment physically limiting their movements as much as possible was seen as the safest way of subduing them—and so the “strait-waistcoat,” as it became known, stepped in to do just that.
Under the name strait-waistcoat, the straitjacket was first recorded in English as far back as 1753, before the more familiar name straitjacket followed on in 1814. Both terms happily coexisted for a time (Dickens even used strait-waistcoat as a verb in his Pickwick Papers in 1837), before straitjacket stepped up to established itself as the usual term towards the turn of the century.
Why did the one word replace the other? It’s difficult to say. Perhaps the change was driven by broader changes in men’s fashions, which made jacket the more popular term overall around the late 1800s, and figuratively consigned the waistcoat to the back of the wardrobe. Or perhaps it was merely that the jacket form of the name made for a snappier, catchier word? Alas, best guesses are all we have here.
One last point worth addressing, though: is it a strait jacket, or a straight jacket?
Straightjacket might be the spelling preferred by [*checks notes*] everyone’s favourite Detroit-based electronic hiphop outfit Quinn XCII of course, but really you can drop that meddlesome gh here.
The “strait” of straitjacket, dire straits and strait-laced is just the same word as in the Straits of Gibraltar. It alludes to narrowness and restriction—so just as a sea strait is a narrow and difficult to navigate passage of water, a dire strait is a distressing situation; someone who is strait-laced is as prim and proper as someone wearing a tightly-fastened stay or bodice; and a straitjacket is one wrapped so snugly around its wearer that it is all but impossible for them to move.