Bow-compass
Bow-compass ({not transcribed}) , noun
1.
An arcograph.
2.
A small pair of compasses, one leg of which carries a pencil, or a pen, for drawing circles. Its legs are often connected by a bow-shaped spring, instead of by a joint.
3.
A pair of compasses, with a bow or arched plate riveted to one of the legs, and passing through the other.