From Latin 'strictus' (drawn tight) via Old French, naming a waterway by its narrowness.
A narrow passage of water connecting two larger bodies of water.
From Old French 'estreit' (narrow), from Latin 'strictus,' past participle of 'stringere' (to draw tight). A strait is etymologically a 'tightened' or narrowed stretch of sea. Key roots: stringere (Latin: "to draw tight, to bind").
A straitjacket is literally a 'tight jacket'—the spelling 'straightjacket' is a folk etymology. The garment has nothing to do with straightness.