Corresponding sides are a pair of matching sides in two different shapes (size does not matter). In the field of geometry, the concept of corresponding sides plays an important role to prove various triangular theorems.
The Boeing B-17 Flying Fortress is a four-engine heavy bomber aircraft developed in the 1930s for the United States Army Air Corps (USAAC).
The definition of a fortress is a secured and strong place. An example of a fortress is a wall made out of stone that protects a city. a fortified place; fort: often used fig.: a mighty fortress is our God.