Go is soybeans that have been soaked in water and then ground down to a paste. Put that paste into miso soup and what you have is gojiru. The name is not a description of the soup. It is the recipe, stated in one syllable.

In Saitama, soybeans were planted along the banks between the paddies. They will grow on poor ground, and the point was not to waste the banks. Beans a household grew there for its own use had their own name: tanokuro-mame, bank beans.

Soy was also grown here as a rotation crop and as a substitute crop in converted paddy, so it was never scarce, and a soup built on it was everyday food rather than anything special.

Into the pot go taro, daikon, carrot, leek, shiitake, konnyaku, and fried tofu. The vegetables simmer in stock, the ground soy goes in, and miso finishes it. It was made after the autumn harvest, as the thing that carried the nutrition of the beans through the cold months when little else was coming in, and it is served now in school lunches and restaurants. Miso is the usual seasoning, though soy sauce or salt is used in some houses. What was grown in the strip of dirt nobody counted as a field turns out to be the main ingredient of the soup.