The terms "odachi" and "nodachi" are sometimes used interchangeably to refer to a large, two-handed Japanese sword with an elongated blade. However, there can be some variation in how the terms are defined, and the distinction between them is not always strictly clear-cut.

In general, "odachi" is the more commonly used term and is often translated as "great sword" or "long sword." Odachi typically refers to a long, single-edged sword with a blade length of around 90 centimeters (35 inches) or longer. It was primarily used by samurai on foot and was known for its reach and cutting power. The odachi was typically wielded with two hands due to its size and weight.

"Nodachi," on the other hand, is sometimes used to refer specifically to a type of odachi with a pronounced curvature along the length of the blade. The term "nodachi" can be translated as "field sword" or "reaping sword." Nodachi blades often had a dramatic curve that facilitated powerful slashing attacks and made them effective against groups of opponents.

However, it's worth noting that the precise definitions and distinctions between odachi and nodachi can vary depending on historical periods, regions, and individual interpretations. Some sources use the terms interchangeably, while others differentiate them based on blade curvature or other characteristics.

In summary, both odachi and nodachi generally refer to large, two-handed Japanese swords with elongated blades. While there can be some variation in how the terms are defined, they are often used to describe similar types of swords that were favored by samurai warriors in ancient Japan.