Sino-Vietnamese vocabulary (, Chữ Hán: 詞漢越, literally 'Chinese-Vietnamese words') is a layer of about 3,000 monosyllabic morphemes of the Vietnamese language borrowed from Literary Chinese with consistent pronunciations based on Middle Chinese. Compounds using these morphemes are used extensively in cultural and technical vocabulary. Together with Sino-Korean and Sino-Japanese vocabularies, Sino-Vietnamese has been used in the reconstruction of the sound categories of Middle Chinese. Samuel Martin grouped the three together as "Sino-xenic". There is also an Old Sino-Vietnamese layer consisting of a few hundred words borrowed individually from Chinese in earlier periods. These words are treated by speakers as native. More recent loans from southern varieties of Chinese, usually names of foodstuffs such as 'Chinese sausage' (from Cantonese), are not treated as Sino-Vietnamese but more direct borrowings.
Estimates of the proportion of words of Chinese origin in the Vietnamese lexicon vary from one third to half and even to 70%. The proportion tends towards the lower end in speech and towards the higher end in technical writing. In the famous dictionary by Vietnamese linguist , about 40% percent of vocabulary are of Chinese origin.
It has also been theorised that Sino-Vietnamese words came from a language shift from a population of Annamese Middle Chinese speakers that lived in Red River Delta in northern Vietnam to proto-Vietic-Muong, as opposed to Sino-Xenic words coming from studious application with limited exposure to spoken Sinitic as Sino-Korean and Sino-Japanese have done. It has also been proposed that Vietnamese is a language derived from a coastal creole that developed from interaction with Middle Chinese and Kri-Molic peoples (Vietic peoples).
Monosyllabic loanwords
As a result of a thousand years of Chinese control, a small number of Chinese words were borrowed into Vietnamese, called Old Sino-Vietnamese layer. Furthermore, a thousand years of use of Literary Chinese after independence, a considerable number of Chinese words were borrowed, called the Sino-Vietnamese layer. These layers were first systematically studied by linguist Wang Li.
Middle Chinese and Vietnamese, like most languages of the Mainland Southeast Asia linguistic area, are analytic languages. Almost all morphemes are monosyllabic and lacking inflection. The phonological structure of their syllables is also similar.
The Old Sino-Vietnamese layer was introduced after the Chinese conquest of the kingdom of Nanyue, including the northern part of Vietnam, in 111 BC. The influence of the Chinese language was particularly felt during the Eastern Han period (25–190 AD), due to increased Chinese immigration and official efforts to sinicize the territory. This layer consists of roughly 400 words, which have been fully assimilated and are treated by Vietnamese speakers as native words.
The much more extensive Sino-Vietnamese proper was introduced with Chinese rhyme dictionaries such as the Qieyun in the late Tang dynasty (618–907). Vietnamese scholars used a systematic rendering of Middle Chinese within the phonology of Vietnamese to derive consistent pronunciations for the entire Chinese lexicon. After driving out the Chinese in 880, the Vietnamese sought to build a state on the Chinese model, including using Literary Chinese for all formal writing, including administration and scholarship, until the early 20th century. Around 3,000 words entered Vietnamese over this period. Some of these were re-introductions of words borrowed at the Old Sino-Vietnamese stage, with different pronunciations due to intervening sound changes in Vietnamese and Chinese, and often with a shift in meaning.
Wang Li followed Henri Maspero in identifying a problematic group of forms with "softened" initials g-, gi, d- and v- as Sino-Vietnamese loans that had been affected by changes in colloquial Vietnamese. Most scholars now follow André-Georges Haudricourt in assigning these words to the Old Sino-Vietnamese layer.
Sino-Vietnamese shows a number of distinctive developments from Middle Chinese: Sino-Vietnamese distinguishes Early Middle Chinese palatal and retroflex sibilants, which are identified in all modern Chinese varieties, and had already merged by the Late Middle Chinese period. Sino-Vietnamese reflects Late Middle Chinese labiodental initials, which were not distinguished from labial stops at the Early Middle Chinese phase. Middle Chinese grade II finals yield a palatal medial -y- like northern Chinese varieties but unlike southern ones. For example, Middle Chinese kæw yields SV , Cantonese gaau and Beijing .