The word "ratchet" can refer to both a mechanical device that allows movement in one direction while preventing it in the opposite direction, and as a slang term that often describes a person or behavior that is perceived as low-class or trashy. In mechanics, a ratchet is commonly used in tools (like a ratchet wrench), where it enables continuous movement without needing to remove the tool from the workpiece.
The word "ratchet" comes from the French word rachette, which is a diminutive form of rache, derived from the Old Provençal raca, meaning to "move backward." It has evolved in English to describe both the mechanical aspect and the more informal usage.