As an adjective strait means 'narrow or cramped' and 'strict or rigorous'： the idea behind strait-laced and straitjacket is of being tightly laced or confined. As strait is now old-fashioned and unfamiliar, however, people often interpret it as the more usual word straight. Straight-laced and straightjacket are now generally accepted in standard English, and the spelling straight-laced is more common than strait-laced in the Oxford English Corpus.