Synonymous Vietnamese Sino - Vietnamese compound words are very special type of words in Vietnamese language. They are the combination of two words of quite different origin, one originates from Chinese language (Sino Vietnamese pronunciation), the other originates from Vietnamese language, but they mean the same or very similar. Through survey and evidence from various sources of documents in different periods. the author suggests that synonymous Vietnamese Sino - Vietnamese compound words dual Vietnamese Sino - Vietnamese synonymous appeared by the thirteenth century, associated with the stable process of Sino-Vietnamese pronunciation of Chinese language and the birth and development of the "Nom" language. Especially, this type of compound word appeared pretty much after the birth of the textbooks of Chinese and "Nom" language written in verse from the second half of the eighteenth century onwards. This proves that synonymous Vietnamese Sino - Vietnamese compound words were invented by Vietnamese people to make it easier and more convenient for learning Chinese language and "Nom" language. This type of compound words is also in accordance with the rule of the development of Vietnamese phonetics, increases the ways of expressing feelings
in addition, it is palatable and easy to remember... so it has been developped increasingly, creating a characteristic of Vietnamese language.