any of various instruments for measuring external or internal dimensions, with either an in-turned or out-turned point and two hinged legs resembling a pair of compasses;
e.g. A caliper can be simply a compass that has either inward or outward-facing points.
(noun)
a car or bicycle brake that had two or more hinged parts;
e.g. Brake calipers are an essential part of getting your car to stop when you hit the brakes.