Voiced labiodental nasal

A voiced labiodental nasal is a type of consonantal sound. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɱ⟩. The IPA symbol is a lowercase letter m with a leftward hook protruding from the lower right of the letter. Occasionally it is instead transcribed as an m with a dental diacritic: ⟨m̪⟩ (for example in extIPA, where the two transcriptions are presented as variants).^[1]

A labiodental pronunciation of [ɱ] is very similar to that of the bilabial nasal [m], but instead of the lips touching each other, the lower lip touches the upper teeth. The position of the lips and teeth is generally the same as for the production of the labiodental fricatives [f] and [v], though air escapes between the lip and the teeth in the case of the fricatives. Ladefoged & Maddieson (1996) note that due to gaps between the incisors, which would allow for additional airflow, it is not known if a 'true occlusive' can occur with this gesture, though it still patterns as one.^[2]

Although commonly appearing in languages, [ɱ] is overwhelmingly an allophone restricted to a position before the labiodental consonants [f] and [v]. A phonemic /ɱ/ has only been reported for the Kukuya language, where it contrasts with /m/ and is "accompanied by strong protrusion of both lips". It is [ɱʷ] before /a/ and [ɱ] before /i/ and /e/, perhaps because labialization is constrained by the spread front vowels; it does not occur before the back (rounded) vowels /o/ and /u/.^[3]

Nonetheless, [ɱ] is extremely common around the world phonetically, as it is the universal allophone of /m/ and a very common allophone of /n/ before the labiodental fricatives [f] and [v], as for example in English comfort and circumvent, and, for many people, infinitive and invent. In the Angami language, [ɱ] occurs as an allophone of /m/ before /ə/. In Drubea, [ɱ] is reported as an allophone of /v/ before nasal vowels.^[4]

A proposal to retire the letter ⟨ɱ⟩ was made in the run-up to the Kiel Convention of 1989, with the labiodental nasal to be transcribed solely by ⟨m̪⟩, but the proposal was defeated in committee.^[5][6] A recommendation by extIPA was retired soon afterwards in response.