Source: In modern use
Trường đao (長刀) literally means "large sword". The trường đao is a type of Vietnamese falchion that is closely related to Chinese dàdāo (大刀). It typically has a long hilt, often wrapped with rattan and a ring pommel. It usually has a small guard and a large blade that flares out considerably.
A typical example. Probably 19th century.
Listed on this site.
Old photographs often show this type of weapons used for decapitations, but this was probably not their sole purpose. I have had matched pairs even, of a smaller and larger example, that suggest they were also worn by fighting men.