bow-compass

from The Century Dictionary.

• noun See compass.

from the GNU version of the Collaborative International Dictionary of English.

• noun An arcograph.
• noun 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.
• noun A pair of compasses, with a bow or arched plate riveted to one of the legs, and passing through the other.