"Lip rounding" redirects here. See Roundedness'' for the lip rounding of vowels.

Labialisation is a secondary articulatory feature of sounds in some languages. Labialized sounds involve the lips while the remainder of the oral cavity produces another sound. The term is normally used to refer to consonants. When vowels involve the lips, they are usually called rounded.

Labialisation may also refer to a type of assimilation process.

Where found

Labialisation is the most widespread secondary articulation in the world's languages. It is phonemically contrastive in the Northwest Caucasian, Athabaskan, and Salishan language families, among others. This contrast is reconstructed also for Proto-Indo-European, the common ancestor of the Indo-European languages.

American English has three degrees of (phonetic) labialization: Fully rounded /w/ and initial /ɹ/, open-rounded , and unrounded, in which vowels are sometimes called spread. These secondary articulations are not universal. For example, while French shares the English open-rounding of while Russian does not have rounding of its postalveolar fricatives ().

Types of labialisation

Out of 706 language inventories surveyed by , labialisation occurred most often with velar (42%) and uvular (15%) segments and least often with dental and alveolar segments. With non-dorsal consonants, labialisation may include velarisation as well. Labialisation is not restricted to lip-rounding. The following articulations have either been described as labialisation, or been found as allophonic realisations of prototypical labialisation:

  • Labial rounding, with or without protrusion of the lips (found in Navajo)
  • Labiodental frication, found in Abkhaz
  • Bilabial frication, found in Ubykh
  • Bilabial trill, found in Ubykh
  • Bilabial plosion, found in Ubykh
  • "Labilialisation" without lip rounding, found in the Iroquois
  • Rounding without velarization, found in Shona and in the Bzyb dialect of Abkhaz

Eastern Arrernte is a language with labialisation at all places and manners of articulation. The labialisation derives historically from adjacent rounded vowels, as is also the case of the Northwest Caucasian languages.


In the International Phonetic Alphabet, labialisation of velar consonants is indicated with a raised w modifier [ʷ] (Unicode U+02B7), as in /kʷ/. (Elsewhere this diacritic generally indicates simultaneous labialization and velarization.) There are also diacritics, respectively , to indicate greater or lesser degrees of rounding. These are normally used with vowels, but may occur with consonants. For example, in the Athabaskan language Hupa, voiceless velar fricatives distinguish three degrees of labialization, transcribed either or .

The Extensions to the IPA has two additional symbols for degrees of rounding: Spread /ɹ͍/ and open-rounded /ʒœ/. It also has a symbol for labialdentalized sounds, /tʋ/.

If precision is desired, the Abkhaz and Ubykh articulations may be transcribed with the appropriate fricative or trill raised as a diacritic: [tv], [tβ], [tʙ], [tp].

For simple labialization, resurrected an old IPA symbol, [ ̫]. However, their chief example is Shona sv and zv, which they transcribe /s̫/ and /z̫/ but which actually seem to be whistled sibilants, without necessarily being labialized. The open rounding of English /ʃ/ is also unvelarized.

Labial assimilation

Labialisation also refers to a specific type of assimilatory process where a given sound become labialised due to the influence of neighboring labial sounds. For example, /k/ may become /kʷ/ in the environment of /o/, or /a/ may become /o/ in the environment of /p/ or /kʷ/.

In the Northwest Caucasian languages as well as some Australian languages rounding has shifted from the vowels to the consonants, producing a wide range of labialized consonants and leaving in some cases only two phonemic vowels. This appears to have been the case in Ubykh and Eastern Arrernte, for example. The labial vowel sounds usually still remain, but only as allophones next to the now-labial consonant sounds.



  • Crowley, Terry. (1997) An Introduction to Historical Linguistics. 3rd edition. Oxford University Press.

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