In linguistics, the term voiceless describes the pronunciation of sounds when the larynx does not vibrate. Phonologically, this is a type of phonation, which contrasts with other states of the larynx, but some object that the word "phonation" implies voicing, and that voicelessness is the lack of phonation. (See phonation for more.)
The International Phonetic Alphabet has distinct letters for many voiceless and modally voiced pairs of consonants (the obstruents), such as [p b], [t d], [k ɡ], [q ɢ] [f v], [s z], and also a diacritic for voicelessness, [ ̥] (the under-ring) that can be used with letters for prototypically voiced sounds, such as vowels and nasal consonants: [ḁ], [n̥]. (The ring is placed above letters with descenders, as with [ŋ̊].)
Voiceless vowels and other sonorants
Sonorants are those sounds, such as vowels and nasal consonants, which are voiced in most of the world's languages. However, in some languages sonorants may be voiceless, usually allophonically. For example, the Japanese word sukiyaki is pronounced [su̥kijaki]. This may sound like [skijaki] to an English speaker, but the lips can be seen compressing for the [u̥]. Something similar happens in English with words like peculiar [pʰə̥ˈkjuːliɚ] and potato [pʰə̥ˈteɪtoʊ].
Sonorants may also be contrastively voiceless, not just voiceless due to their environment. Tibetan, for example, has a voiceless /l̥/ in Lhasa, which sounds similar to, but is not as noisy as, the voiceless lateral fricative /ɬ/ in Welsh, and which contrasts with a modally voiced /l/. Welsh contrasts several voiceless sonorants: /m, m̥/, /n, n̥/, /ŋ, ŋ̊/, and /r, r̥/, the latter represented by "rh".
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