The biggest samurai sword is known as the Ōdachi. The term Ōdachi translates to "big sword" or "great sword." It refers to a type of Japanese sword with an exceptionally long blade. The Ōdachi is characterized by its immense size, often exceeding 90 centimeters (35 inches) in blade length and sometimes reaching over 100 centimeters (39 inches).

The Ōdachi was primarily used during ancient and medieval times in Japan. Due to its size and weight, it required the use of both hands to wield effectively. The Ōdachi was typically used in specific battle situations or as ceremonial weapons, often carried by high-ranking samurai or displayed in temples and shrines.

The large size of the Ōdachi allowed for powerful and wide sweeping strikes, capable of inflicting significant damage on multiple opponents. However, due to its size and weight, the Ōdachi was not practical for everyday combat or dueling.

Surviving examples of Ōdachi can be found in museums, temples, and historical collections, where they are admired for their impressive size and historical significance. The Ōdachi represents an extreme example of a samurai sword and showcases the craftsmanship and skills of ancient Japanese swordsmiths.