A fricative is a consonant produced by forcing air through a narrow channel made by placing two articulators close together.[1] These may be the lower lip against the upper teeth, in the case of [f]; the back of the tongue against the soft palate in the case of German [x] (the final consonant of Bach); or the side of the tongue against the molars, in the case of Welsh [ɬ] (appearing twice in the name Llanelli). This turbulent airflow is called frication.[2]
A particular subset of fricatives are the sibilants. When forming a sibilant, one still is forcing air through a narrow channel, but in addition, the tongue is curled lengthwise to direct the air over the edge of the teeth.[1] English [s], [z], [ʃ], and [ʒ] are examples of sibilants.
The usage of two other terms is less standardized: "Spirant" is an older term for fricatives used by some American and European phoneticians and phonologists.[3] "Strident" could mean just "sibilant", but some authors[who?] include also labiodental and uvular fricatives in the class.
The airflow is not completely stopped in the production of fricative consonants. In other words, the airflow experiences friction.
All sibilants are coronal, but may be dental, alveolar, postalveolar, or palatal (retroflex) within that range. However, at the postalveolar place of articulation, the tongue may take several shapes: domed, laminal, or apical, and each of these is given a separate symbol and a separate name. Prototypical retroflexes are subapical and palatal, but they are usually written with the same symbol as the apical postalveolars. The alveolars and dentals may also be either apical or laminal, but this difference is indicated with diacritics rather than with separate symbols.
The lateral fricative occurs as the ll of Welsh, as in Lloyd, Llewelyn, and Machynlleth ([maˈxənɬɛθ], a town), as the unvoiced 'hl' and voiced 'dl' or 'dhl' in the several languages of Southern Africa (such as Xhosa and Zulu), and in Mongolian.