This revision of the alphabet eliminated uppercase forms, so there was no conflict between ɖ and đ. Đ was used in Medieval Latin to mark abbreviations of words containing the letter d. For example, hđum could stand for heredum "of the heirs".

[8] Whereas D is pronounced as some sort of dental or alveolar stop in most Latin alphabets, an unadorned D in Vietnamese represents either /z/ (Hanoian) or /j/ (Saigonese).

The Vietnamese alphabet was formally described for the first time in the 17th-century text Manuductio ad Linguam Tunckinensem, attributed to a Portuguese Jesuit missionary, possibly Francisco de Pina[9] or Filipe Sibin.

[10] This passage about the letter Đ was later incorporated into Alexandre de Rhodes' seminal Dictionarium Annamiticum Lusitanum et Latinum:[11] Another letter written with the symbol đ is completely different than our own and is pronounced by raising the tip of the tongue to the palate of the mouth, immediately removing it, without in any way touching the teeth, for example đa đa: partridge.

[contradictory] It is rarely typed, but commonly used on signs and in handwritten text.The lowercase đ is used in some phonetic transcription schemes to represent a voiced dental fricative [ð] (English th in this).

Eth (ð) is more commonly used for this purpose, but the crossed d has the advantage of being able to be typed on a standard typewriter, by overlaying a hyphen over a d.[15] A minuscule form of the letter, đ, is the symbol of the đồng, the currency of Vietnam, by a 1953 decree by Hồ Chí Minh.

In Unicode, the Vietnamese đồng symbol is properly represented by U+20AB ₫ DONG SIGN, but U+0111 đ LATIN SMALL LETTER D WITH STROKE is often used instead.

Dispersity is represented by the symbol Đ, and is a measure of the heterogeneity of sizes of molecules or particles in a mixture, referring to either molecular mass or degree of polymerization.

[1] Unicode has a distinct code point for the visually very similar capital eth, Ð, U+00D0, which can lead to confusion.

As paraphrased by de Rhodes:[12] ...estque vitium linguæ, aliud đ notatur eo signo quia est omninò diversum à nostro & pronunciatur attollendo extremum linguæ ad palatum oris, illamque statim amovendo, absque eo quod ullo modo dentes attingat ut đa đa, perdix: & hæc litera est valdè in usu in principio dictionis.