labial (adj./n.)

A general term in the PHONETIC classification of speech sounds on the basis of their PLACE OF ARTICULATION: it refers to active use of one lip (as in LABIO-DENTAL sounds, such as [f]) or both lips (as in BILABIAL CONSONANTS, such as [b], or ROUNDED VOWELS, such as [u]). In an empty sense, all ORAL sounds are labial, in that the airflow has to pass through the lips: the important qualification in the above definition is that the lips are actively involved. From a position of rest, there must be a marked movement to qualify as a labial sound (‘a labial’), and it is lip-rounding which is the most common and noticeable feature.

Similarly, labialization is a general term referring to a SECONDARY ARTICULATION involving any noticeable lip-rounding, as in the initial [k] of coop, or sh- of shoe, which are here labialized, because of the influence of the labialization in the following vowel [u]. Labialization is applied both to cases where the lip-rounding is an essential feature of a sound’s identity, as in [u], and to cases where the lip-rounding is found only in specific contexts, as in the [k] example above – in kill, there is no labialization. The DIACRITIC for labialization is [w], underneath the main symbol, but a raised [^w] is often used. The term has developed a special status in phonological theory, especially in various NON-LINEAR models. For example, in ARTICULATOR-BASED FEATURE THEORY, it refers to a single-valued NODE involving the lips as an active articulator. In CONSTRICTION-based models, it is defined as a constriction formed by the lower lip.