Historically the cutlass was normally used much like a machete, hacking through tough material such as wood or heavy rope. Its durability and size made it an effective weapon in the cramped confines of a ship. This may explain why the Nami Solo is classified as such.
The Codex entry of the Nami Solo uses the stance used to showcase most one-handed weaponry, but its short hilt results in your Warframe's left hand grasping at nothing.
Just like Nami Skyla, the word Nami (波) means "wave" in Japanese.