In terms of size, the terms "odachi" and "nodachi" are often used interchangeably and can refer to large Japanese swords with exceptionally long blades. Both the odachi and nodachi typically exceed the standard length of a katana and are characterized by their extended reach and two-handed wielding.

However, there is a slight difference in the historical usage and connotations associated with the terms:

1. Odachi: The term "odachi" translates to "big sword" or "great sword." It was primarily used to refer to large swords wielded by foot soldiers and cavalry during ancient and medieval Japan. The odachi was renowned for its size and cutting power, and its length could range from around 150 centimeters (59 inches) to over 200 centimeters (79 inches). The odachi is generally associated with earlier periods of Japanese history.
2. Nodachi: The term "nodachi" translates to "field sword" or "field longsword." It is a term used to describe large swords, often with an emphasis on its use by foot soldiers in open battlefields. The nodachi typically refers to swords with a length ranging from approximately 90 centimeters (35 inches) to over 120 centimeters (47 inches). The nodachi is associated with later periods of Japanese history.

In essence, while there is some overlap between the terms "odachi" and "nodachi" in terms of size, the historical usage and connotations can vary. Both terms generally refer to large swords with long blades, but the specific context and historical period can influence their usage.