Sibilants (from Latin: sībilāns : 'hissing') are fricative consonants of higher amplitude and pitch, made by directing a stream of air with the tongue towards the teeth.
[1] Examples of sibilants are the consonants at the beginning of the English words sip, zip, ship, and genre.
In the alveolar hissing sibilants [s] and [z], the back of the tongue forms a narrow channel (is grooved) to focus the stream of air more intensely, resulting in a high pitch.
With the hushing sibilants (occasionally termed shibilants), such as English [ʃ], [tʃ], [ʒ], and [dʒ], the tongue is flatter, and the resulting pitch lower.
[4][5] Some linguistics use the terms stridents and sibilants interchangeably to refer to the greater amplitude and pitch compared to other fricatives.
This distinction is particularly important for retroflex sibilants, because all three varieties can occur, with noticeably different sound qualities.
For tongue-down laminal articulations, an additional distinction can be made depending on where exactly behind the lower teeth the tongue tip is placed.
When the tip of the tongue rests against the lower teeth, there is no sublingual cavity, resulting in a sharper sound.
Ladefoged and Maddieson[1] term this a "closed laminal postalveolar" articulation, and transcribe them (following Catford) as [ŝ, ẑ], although this is not an IPA notation.
The following table shows the types of sibilant fricatives defined in the International Phonetic Alphabet: Diacritics can be used for finer detail.
There is no diacritic to denote the laminal "closed" articulation of palato-alveolars in the Northwest Caucasian languages, but they are sometimes provisionally transcribed as [ŝ ẑ].
Also, Ladefoged has resurrected an obsolete IPA symbol, the under dot, to indicate apical postalveolar (normally included in the category of retroflex consonants), and that notation is used here.
The whistled sibilants of Shona have been variously described—as labialized but not velarized, as retroflex, etc., but none of these features are required for the sounds.
Besides Shona, whistled sibilants have been reported as phonemes in Kalanga, Tsonga, Changana, Tswa—all of which are Southern African languages—and Tabasaran.
In Changana, the lips are rounded (protruded), but so is /s/ in the sequence /usu/, so there is evidently some distinct phonetic phenomenon occurring here that has yet to be formally identified and described.
[citation needed] Toda also has a four-way sibilant distinction, with one alveolar, one palato-alveolar, and two retroflex (apical postalveolar and subapical palatal).
That occurs in southern Peninsular Spanish dialects of the "ceceo" type, which have replaced the former hissing fricative with [θ], leaving only [tʃ].
However, they do not have the grooved articulation and high frequencies of other sibilants, and most phoneticians[1] continue to group them together with bilabial [ɸ], [β] and (inter)dental [θ], [ð] as non-sibilant anterior fricatives.
The nature of sibilants as so-called 'obstacle fricatives' is complicated – there is a continuum of possibilities relating to the angle at which the jet of air may strike an obstacle.
The grooving often considered necessary for classification as a sibilant has been observed in ultrasound studies of the tongue for the supposedly non-sibilant voiceless alveolar fricative [θ̠] of English.