noun Usually cross hairs.
Examples from the Web for cross hair
Historical Examples of cross hair
The "radius of measurement" is the distance between the front face of the revolving mirror and the cross-hair of the micrometer.
Then the screw was turned till the cross-hair bisected the deflected image of the slit.
After the cross-hair indicators and the level have been attached to the camera, adjustments are necessary.The Boy Mechanic, Book 2