Ḍād(ﺽ ), is one of the six letters the Arabic alphabet added to the twenty-two inherited from the Phoenician alphabet (the others being *ṯāʾ *, *ḫāʾ *, *ḏāl *, *ẓāʾ *, *ġayn *). In name and shape, it is a variant of *ṣād *.Its numerical value is 800 (see Abjad numerals).

The sound it represented at the time of the introduction of the Arabic alphabet is somewhat uncertain, likely a pharyngealized voiced alveolar lateral fricative or a similar affricated sound [ d͡ɮˤ ] or [ dˡˤ ].^[1]In contemporary Arabic, it may represent a pharyngealized voiced alveolar stop , pharyngealized voiced dental stop [ d̪ˤ ] or velarized voiced dental stop [ d̪ˠ ].^[2]

Based on ancient descriptions of this sound, it is clear that in Qur’anic Arabicḍwas some sort of unusual lateral sound.^{[2][1][3][-1][5]}Sibawayh, author of the first book on Arabic grammar, explained the letter as being articulated from “between the first part of the side of the tongue and the adjoining molars”. It is reconstructed by modern linguists as having been either a pharyngealized voiced alveolar lateral fricative or a similar affricated sound [ d͡ɮˤ ] or [ dˡˤ ].^[1][3]The affricated form is suggested by loans ofḍinto Akkadian asldorlṭand into Malaysian asdl.^[2]However, not all linguists agree on this; the French orientalist André Roman supposes that the letter was actually a voiced emphatic alveolo-palatal sibilant / ʑˤ /, similar to the Polish *ź *.^[1][3]

This is an extremely unusual sound, and led the early Arabic grammarians to describe Arabic as the لغة الضادlughat aḍ-ḍād“the language of theḍād“, since the sound was thought to be unique to Arabic.

^[2]The emphatic lateral nature of this sound is possibly inherited from Proto-Semitic, and is compared to a phoneme in South Semitic languages such as Mehri (where it is usually an ejective lateral fricative). The corresponding letter in the South Arabian alphabet isṣ́, and in Ge’ez alphabetṢ́appaፀ ), although in Ge’ez it merged early on withṣ.

The reconstruction of Proto-Semitic phonology includes an emphatic voiceless alveolar lateral fricative [ ɬʼ ] or affricate [ t͡ɬʼ ] forṣ́. This sound is considered to be the direct ancestor of Arabicḍād, while merging withṣādin most other Semitic languages.

The letter itself is distinguished a derivation, by addition of a diacritic dot, from صṣād(representing /sˤ/).

The standard pronunciation of this letter in modern Standard Arabic is the “emphatic” /d/: pharyngealized voiced alveolar stop , pharyngealized voiced dental stop [ d̪ˤ ] or velarized voiced dental stop [ d̪ˠ ].^[2]

In most Bedouin influenced Arabic vernaculars ضḍādand ظ *ẓāʾ * have been merged quite early.^[1]like in the varieties (such as Bedouin and Iraqi), where the dental fricatives are preserved, both the letters are pronounced /ðˤ/.^[1][3][5]However, there are dialects in South Arabia and in Mauritania where both the letters are kept different but not in all contexts.^[1]In other vernaculars such as Egyptian the distinction between ضḍādand ظ *ẓāʾ * is most of the time made; but Classical Arabicẓāʾoften becomes /zˤ/, e.g.ʿaẓīm(< Classical عظيمʿaḏ̣īm) “great”.^[1][3][6]

“De-emphaticized” pronunciation of the both letters in the form of the plain /z/ entered into other non-Arabic languages such as Persian, Urdu, Turkish.

^[1]However, there do exist Arabic borrowings into Ibero-Romance languages as well as Hausa and Malay, whereḍādandẓāʾare differentiated.^[1]

ض is transliterated asḍ(D with underdot) in romanization.

When transliterating Arabic in the Hebrew alphabet, it is either written as ד ‬ (the letter for / d /) or as צ׳‬ (*tsadi * with geresh).