Old English rodd "a rod, pole," which is probably cognate with Old Norse rudda "club," from Proto-Germanic *rudd- "stick, club," from PIE *reudh- "to clear land."
As a long, tapering elastic pole for fishing, from mid-15c. Figurative sense of "offshoot" (mid-15c.) led to Biblical meaning "scion, tribe." As an instrument of punishment, attested from mid-12c.; also used figuratively for "any sort of correction or punishment," but the basic notion is of beating someone with a stick.
As a unit of measure (5½ yards or 16½ feet, also called perch or pole) first attested mid-15c., from the stick used to measure it off. As a measure of area, "a square perch," from late 15c., the usual measure in brickwork. Meaning "light-sensitive cell in a retina" is from 1866, so-called for its shape. Slang meaning "penis" is recorded from 1902; that of "gun, revolver" is from 1903.
A straight slender cylindrical formation.
A rod cell.
An elongated bacterium; a bacillus.
One of the rod-shaped cells in the retina of the eye of many vertebrate animals. Rods are more sensitive to light than cones and are responsible for the ability to see in dim light. However, rods are insensitive to red wavelengths of light and do not contribute greatly to the perception of color. Compare cone.