1911 Encyclopædia Britannica/Rod
ROD (O.E. rodd, probably related to Norw. rudda, stick, rodda, stake), a twig or shoot of a tree or bush, especially a straight slender stick or wand used as an instrument of punishment, as a symbol of office, or as an implement, usually composed of several joints, for angling or fishing. The term is thus applied to a metal bar, slender in proportion to its length, used as a tie, brace or connecting shaft between different parts of a machine. It is familiar in the titles, showing the colour of their wands of office, of the gentlemen ushers of the three principal British orders of knighthood, the ushers of the Garter and St Patrick being “Ushers of the Black Rod,” and of the Thistle “Green Rod.” The use of a rod as a measuring implement has given rise to the use of the word for a measure of length = 5½ yds. or 162½ ft.; this length is also named a pole or perch, the origin of the application being the same as in “rod”; as a measure of area, a rod = a square pole or perch, 30¼ square yds.= 272¼ square ft., 160 rods = 1 acre.