(anatomy) Any of the cylindrical photoreceptor cells in the retina that function in dim light levels.

A rod or piece of iron used to ascertain the depth of water in a ship's hold. It is let down in a groove by a pump. / A probe used in urethral sounding

plural of piston rod

Any of a number of steel tubes, containing boron or other neutron absorber, that are inserted into the core of a nuclear reactor in order to control its rate of reaction

A long zirconium tube, filled with pellets of uranium oxide, stacked in bundles inside a nuclear reactor as fuel.

plural of picture rod

A rod or metal tube fixed to the wall of a room, used for hanging pictures.

plural of fit rod

(shipbuilding) A gauge rod used to try the depth of a bolt hole in order to determine the length of bolt required.

A graduated staff, typically having alternate black and white sections, used (along with a theodolite) in surveying