Why are brothers-in-law called brothers-in-law?

In Vietnamese, both the phrases “anh em cot cheo” and “anh em dong hao” refer to men who are sons-in-law in the same family, meaning their wives are sisters.

Why are they called brothers?

The term "row post" or "row mast" refers to the post on the side of the boat used to tie the oars. The oar post is nailed to the bow and stern of the boat, serving as a post to attach the oars to. Usually, the tie must be strong, but the tie at the oar post is very loose, mainly to make the oars easy to paddle in the water, just like the relationship between brothers-in-law is often not very close.

The term "brothers of the rowing boat" is strongly associated with the river and is said to originate from the life of people in the South, where there are many rivers and canals, and traveling by boat is very popular.

Regarding the phrase "brothers of the same family", many people explain that "dong hao" is the name of a wild vegetable with very shallow roots, very easy to pull out, just a light pull can pull out a bunch of roots. This image also implies that the relationship between two brothers-in-law is very loose, can easily separate. This is the way people in the North call it, where this type of vegetable is abundant.

In fact, the relationship between brothers-in-law in Vietnamese families is not as close as that between sisters-in-law. Vietnamese people have a saying "daughter-in-law, son-in-law, guest"; daughters-in-law have many obligations to their husband's family, so they meet and interact more often, both on normal days and when the family has events, have more interactions and also influence each other's lives more. Meanwhile, sons-in-law often have fewer obligations, less opportunities to appear together, so the relationship is also loose.

However, this is only relative, whether the family relationship is close or cold depends on how each family treats each other. In many families, the brothers are really friends, close brothers, together building a warm family, sharing the burden of difficult tasks when the wife's parents need it.