Grocery stores are big or little. Supermarkets are grocery stores. Supermarkets are only large.

Although in common usage the words are used as though they are the same, the distinction between them is size. Grocery store is a general term. While a supermarket is a grocery store, a grocery store is not always a supermarket. A supermarket is very large and usually has a variety of departments that wouldn't be found in a smaller grocery store; pharmacy, post office, fast food, walk-in clinic, etc. I hope that helps. :) Jack

A grocery store is usually smaller than a supermarket [ In Australia]

Before WWII many towns had small grocery stores only. In my town every few blocks there was a small store that sold food, mostly to the people in the immediate neighborhood. Within a four or five block radius of my house there were four grocery stores. There were no large stores. Some stores employed a delivery boy with a bicycle to deliver the groceries to the customer after the customer had called in his needs by phone. The storekeeper kept a record of the customer's purchases and the customer paid about once a month. After the war, larger stores with a much greater variey of food began to appear. Moreover, since people were becoming more mobile, since they began to buy cars, they did not have to shop only in their own neighborhood, but could go anywhere in town. Since the smaller grocery stores could not compete with the larger ones, they gradually disappeared. Supermarkets began to sell, in addition to food, many items previously sold in department stores. In the early days of supermarkets, there was a one-way turnstile through which a person entered the food section and the exit was only at the cash register. For a while the turnstile was the symbol of a supermarket. Turnstiles have long since disappeared. You'll probably hear the words "grocery store" used only by those of older generations.