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In phonetics and phonology, a retroflex stop is a type of consonantal sound, made with the tongue curled back and in contact with area behind the alveolar ridge or with the hard palate (hence retroflex), held tightly enough to block the passage of air (hence a stop consonant). The point of contact is commonly either the tongue tip or tongue blade (the portion just behind the tip).^[1]

Sometimes, however, the tongue is curled far enough back that the underside actually contacts the palate. That is known as a subapical retroflex stop and particularly occurs in the Dravidian languages of southern India. A stop consonant that is made with the body of the tongue in contact with the hard palate is called a palatal stop.

Retroflex stops are less common than velar stops or alveolar stops and do not occur in Western English. They sound somewhat like the Western English alveolar stops [t] and [d], but they have a more hollow quality. Retroflex stops are particularly common in the South Asian languages, such as Hindi and Tamil, and thus also in Indian English in place of the alveolar stops in other varieties of English. Although they are fairly rare in European languages, they occur in Swedish and Norwegian, as well as in some Southern dialects of Italy, such as in varieties of Sicilian, Calabrian, and Sardinian.

The most common sounds are the stops [ʈ] and [ɖ]. More generally, several kinds are distinguished:

• [ʈ], voiceless retroflex stop
• [ɖ], voiced retroflex stop
• [ʈʼ], retroflex ejective (rare)
• [ᶑ], voiced retroflex implosive (extremely rare or nonexistent)
• [ᶑ̥] or [ʈʼ↓] voiceless retroflex implosive (almost certainly nonexistent)

• Hamann, Silke (January 2008). "How do voiced retroflex stops evolve? Evidence from typology and an articulatory study". ZAS Papers in Linguistics. 49: 97–130. Retrieved 17 April 2019.
• Hamann, Silke (2003). The Phonetics and Phonology of Retroflexes (PDF). LOT. ISBN 90-76864-39-X.