The Vietnamese tilde, also known by its Latin name of apex, was a curved diacritic used in the 17th century to mark final nasalization in the early Vietnamese alphabet.[1] It was an adoption of the Portuguese tilde, and should not be confused with the tone mark ngã, which is encoded as a tilde in Unicode (and in Vietnamese derivatives of ISO-8859-1 such as VISCII, VPS or Windows-1258), despite actually being an adoption of the Greek perispomeni.[2][4]Apex is the name used in contemporary Latin texts.
The third sign, finally, is the apex, which in this language is entirely necessary because of a difference in the ending [i.e. of a word], which the apex makes entirely distinct from the ending that m or n makes, with a meaning entirely diverse in words in which it is employed. However, this sign, namely the apex, only affects o᷃ and u᷃, at the end of a word, as ao᷃ "bee", ou᷃ "grandfather" or "lord". It is pronounced, however, such that neither the lips touch together nor the tongue touches the palate.
— Dictionarium Annamiticum Lusitanum et Latinum[8]
The apex appears atop ⟨o⟩, ⟨u⟩, and less commonly ⟨ơ⟩. As with other accent marks, a tone mark can appear atop the apex.[9]
According to canon law historian Roland Jacques, the apex indicated a final labial-velar nasal[ŋ͡m], an allophone of /ŋ/ that is peculiar to the Hanoi dialect to the present day. The apex apparently fell out of use during the mid-18th century, being unified with ⟨-ng⟩ (representing /ŋ/), in a major simplification of the orthography, though the Vietnamese JesuitPhilipphê Bỉnh (Philiphê do Rosario) continued to use the old orthography into the early 19th century.[10] In Pierre Pigneau de Behaine and Jean-Louis Taberd's 1838 Dictionarium Anamitico-Latinum,[11] the words ao᷃ and ou᷃ became ong and ông, respectively.
The Middle Vietnamese apex is known as dấu sóng or dấu lưỡi câu in modern Vietnamese. The apex is often mistaken for a tilde in modern reproductions of early Vietnamese writing, such as in Phạm Thế Ngũ's Việt Nam văn học sử.[12][13]
^Jacques, Roland (2002). Portuguese Pioneers of Vietnamese Linguistics. Bangkok: Orchid Press. p. 91. The accent mark written by the amanuensis on the first word can be read as the apex (or tilde), an abbreviation sign used in 17th and 18th century Quốc Ngữ to represent the rounded nasal finals: '-aõ' (spelt today '-ong'); '-oũ' (= '-ông'), and '-ũ' (= '-ung'). Thus 'chã' would stand for the word presently spelt 'chẳng.' Note that de Rhodes called the tilde a "circumflex".
^Nguyen, Minh; Miller, Kirk (2024-04-05). "Conflict with the Unicode tilde"(PDF). Annotation request for Vietnamese apex. pp. 2–3. UTC L2/24-111. [Note that equating specifically U+1DD1 with the Vietnamese Apex, as proposed in that document, was opposed by the Medieval Unicode Font Initiative.][3]
^Phạm Thế Ngũ (1961). Việt Nam Văn Học Sử: Giản Ước Tân Biên [History of Vietnamese Literature: New Survey] (in Vietnamese). Saigon: Quốc Học Tùng Thư. p. 61 – via Google Books.