The voiceless bidental fricative is a rare consonantal sound used in some languages. The only natural language known to use it is the Shapsug dialect of Adyghe. It is also used for a geminate voiceless glottal fricative (so phonemically /hː/) in the original version of the constructed language Ithkuil, its offshoot Ilaksh, and the new version of Ithkuil as one of two allophones. For example [h̪͆œʒ] and [čî’yohh] .
Features
Features of the voiceless bidental fricative:
References
Voiceless bidental fricative Wikipedia(Text) CC BY-SA