trammel

Trammel is a term with several distinct meanings in English. In historical usage, it denotes a device used to restrain movement, such as a fetter or bar that limits a captive's or animal's range. The verb to trammel means to hamper, impede, or restrain.

In drafting and geometry, the trammel, also called the ellipsograph, is a mechanism for tracing ellipses. It consists of two sliding carriers constrained to move on perpendicular tracks. A rod attached to the carriers carries a pencil; the point traces an ellipse because of the fixed distances from the pegs to the tracing point. The device is notable for producing precise conic sections and was described in classical texts as a practical instrument.

In carpentry and metalworking, the term trammel also refers to a device used with a beam compass to draw circles and arcs. The components can be adjusted to locate the drawing point at a given radius, enabling precise circle layouts.

Etymology: The term derives from French tramme, from Latin trahere, meaning to drag or draw, reflecting the sense of restraining or drawing tight. In modern usage, to trammel can mean to hamper, constrain, or impede.