ETYM The same word as rood. Related to Rood.
1. A long thin implement made of metal or wood.
2. Any rod-shaped bacterium.
3. Visual receptor cell sensitive to dim light; SYN. rod cell, retinal rod.
A type of light-sensitive cell in the retina of most vertebrates. Rods are highly sensitive and provide only black and white vision. They are used when lighting conditions are poor and are the only type of visual cell found in animals active at night.