A syllabic consonant or vocalic consonant is a consonant that forms a syllable on its own, like the m, n and l in some pronunciations of the English words rhythm, button and bottle. To represent it, the understroke diacritic in the International Phonetic Alphabet (IPA) is used, ⟨U+0329 ◌̩ COMBINING VERTICAL LINE BELOW⟩. It may be instead represented by an overstroke, ⟨U+030D ◌̍ COMBINING VERTICAL LINE ABOVE⟩ if the symbol that it modifies has a descender, such as in [ŋ̍].
Syllabic consonants in most languages are sonorants, such as nasals and liquids. Very few have syllabic obstruents, such as stops and fricatives in normal words, but English has syllabic fricatives in paralinguistic words like shh! and zzz.
In many varieties of High and Low German, pronouncing syllabic consonants may be considered a shibboleth. In High German and Tweants (a Low Saxon dialect spoken in the Netherlands, more Low Saxon dialects have the syllabic consonant), all word-final syllables in infinite verbs and feminine plural nouns spelled -en are pronounced with syllabic consonants. The High German infinitive laufen (to walk) is pronounced [ˈlaʊfn̩] or (in some accents) even [ˈlaʊfɱ̍] and its Tweants counterpart loopn is pronounced [ˈlɔːʔm̩]. Tweants scholars even debate whether or not this feature should be incorporated in spelling, resulting in two generally accepted spelling forms (either loopn or lopen).
Many dialects of English may use syllabic consonants in words such as even [ˈiːvn̩], awful [ˈɔːfɫ̩] and rhythm [ˈɹɪðm̩], which English dictionaries' respelling systems usually treat as realizations of underlying sequences of schwa and a consonant (/ˈiːvən/).
In Danish, a syllabic consonant is the standard colloquial realization of combinations of the phoneme schwa /ə/ and a sonorant, generally referred to as schwa-assimilation, e.g. katten (the cat) /ˈkatən/ = [ˈkʰætn̩], dame (lady) /ˈdaːmə/ = [ˈtɛːm̩], cykel (bike) /ˈsykəl/ = [ˈsykl̩], myre (ant) /ˈmyːrə/ = [ˈmyːɐ], sove (sleep) /ˈsɒːʋə/ = [ˈsɒːʊ], reje (shrimp) /ˈraːjə/ = [ˈʁɑːɪ], huset (the house) /ˈhuːˀsəð/ = [ˈhuːˀsð̩ˠ].
In all four dialect groups of Norwegian, a syllabic alveolar nasal, /n/, may be heard. It is syllabic when following other alveolar consonants and occurs most often in the definite singular form of masculine nouns (see Norwegian grammar) where the schwa has elided, e.g. bilen (the car) [biː.ln̩], where it was originally [biː.lən]. With some speakers, the schwa may be reinserted, especially for words already ending in /n/ where the syllabic /n/ may have been entirely elided afterward, e.g. mannen (the man) can either be pronounced like [mɑ.nn̩], [mɑn] or [man.nən]. In addition to this, a syllabic /n/ always occurs in words like vatn (water) [ʋa.tn̩] and botn (bottom) [bɔ.tn̩]. This syllabification of alveolar nasals also appears in some Swedish dialects[which?]. In all cases where the alveolar sound becomes retroflex, /n/ also becomes retroflex /ɳ/, e.g. barten (the moustache) [ba.ʈɳ̩] (see Norwegian phonology#Consonants). In some Norwegian dialects, a syllabic alveolar lateral approximant /l/ may be heard in the same circumstances as syllabic /n/, e.g. puddel (poodle) [pʉ.dl̩], though it is not as common as syllabic /n/. A syllabic /l/ may also be heard in Bergen, where a following syllabic /n/ has elided completely, e.g. solen (the sun) [suː.l̩]. In dialects that have palatalisation of some alveolar consonants like Northern Norwegian and Trøndersk, the following syllabic /n/ is also palatalised, e.g. ballen (the ball) [ba.ʎɲ̩].
All of the consonants syllabicized in Germanic languages are sonorants. However, the only time obstruents are used syllabically in English is in onomatopoeia, such as sh! [ ʃ̩ː] (a command to be quiet), sss [s̩ː] (the hiss of a snake), zzz [z̩ː] (the sound of a bee buzzing or someone sleeping), and tsk tsk! [ǀǀ] (used to express disapproval or pity), though it is not certain how to define what a syllable is in such cases.
Sanskrit ऋ ṛ [r̩], ऌ ḷ [l̩] & अं ṃ [m̩] are syllabic consonants, allophones of consonantal r and l. This continues the reconstructed situation of Proto-Indo-European, where both liquids and nasals had syllabic allophones, r̩, l̩, m̩, n̩.
Many Slavic languages allow syllabic consonants. Some examples include:
Several Sinitic languages, such as Cantonese and Hokkien, feature both syllabic m ([m̩]) and ng ([ŋ̍]) that stand alone as their own words. In Cantonese, the former is most often used in the word meaning 'not' (唔, [m̭̍]) while the latter can be seen in the word for 'five' (五, [ŋ̬̍]) and the surname Ng (吳, [ŋ̭̍] or 伍, [ŋ̬̍], depending on the tone), among others.
A number of languages have syllabic fricatives or fricative vowels. In several varieties of Chinese, certain high vowels following fricatives or affricates are pronounced as extensions of those sounds, with voicing added (if not already present) and a vowel pronounced while the tongue and teeth remain in the same position as for the preceding consonant, leading to the turbulence of a fricative carrying over into the vowel. In Mandarin Chinese, this happens for example with sī, shī, and rī. Traditional grammars describing them as having a "buzzing" sound. A number of modern linguists describe them as true syllabic fricatives, although with weak frication. They are accordingly transcribed ⟨sź̩, ʂʐ̩́, and ʐʐ̩́⟩ respectively.
However, for many speakers, the friction carries over only into the beginning of the vowel. The tongue and teeth remain where they were, but the tongue contact is lessened a bit to allow for a high approximant vowel with no frication except at the beginning, during the transition. John Wells uses the detailed transcriptions ⟨sz̞ᵚ⟩ for si and ⟨ʂʐ̩ᶤ⟩ for shi (ignoring the tone), with the superscript indicating the "color" of the sound and a lowering diacritic on the z to indicate that the tongue contact is relaxed enough to prevent frication. Another researcher suggests ⟨s͡ɯ⟩ and ⟨ʂ͡ɨ⟩ for si and shi, respectively, to indicate that the frication of the consonant may extend onto the vowel. Some speakers have even more lax articulation, opening the teeth and noticeably lowering the tongue, so that sī shī rī are pronounced [sɯ́ ʂɯ́ ʐɯ́], with the same vowel [ɯ] in each case and no r-coloring.
The Nuosu language has two similar "buzzed" vowels that are described as syllabic fricatives, [β̩, ɹ̝̍]. The former may even be trilled [ʙ̞̍].
Sinologists and linguists working in the Chinese analytical tradition frequently use the term apical vowel (舌尖元音 Shéjiān yuán yīn) to describe the sounds above and others like them in various Sino-Tibetan languages. However, this is a misnomer, as the tongue is actually laminal. The nonstandard symbols ⟨ɿ ʅ ʮ ʯ⟩ are commonly used to transcribe these vowels in place of ⟨z̩ ʐ̩ z̩ʷ ʐ̩ʷ⟩ or ⟨C͡ɯ C͡ɨ C͡u C͡ʉ⟩, respectively. The term apical vowel should also not be taken as synonymous with syllabic fricative, as e.g., the bilabial syllabic fricative [β̩] in Liangshan Yi is not pronounced with the tongue.
Berber, Salish, Wakashan and Chemakuan languages have syllabic obstruents in normal vocabulary, such as Nuxálk [p̍ʰ.t̩ʰ.k̩ʰ.ts̩ʰ], [s̩.pʰs̩] "northeast wind", [ɬ̩.q̍ʰ] "wet", [ť̩.ɬ̩.ɬ̩] "dry", or [nu.jam.ɬ̩] "we (ɬ̩) used to sing (nu.jam.ɬ̩)".
In Standard Yoruba, the consonants m and n may be syllabic and carry tone like vowels. However, they always stand alone as syllables and cannot stand as syllable nuclei.
In Baoulé, m or n may be syllabic. As a stand-alone word, it means "I" (first person subject pronoun), as in N ti baule [n̩̄ tɪ̄ bāūlē] "I speak Baoulé". Its quality varies with the consonant following it, as in M bá aiman [m̩̄ bá āɪ̄mān] "I will come tomorrow".
The Hungarian word s [ʃ̩], a high-register variant of és "and", is a syllabic consonant, although it usually cliticises: s ettem /ʃ̩ ɛtːɛm/ [ʃɛtːɛm] "and I had eaten".