The voiced dental fricative is a consonant sound used in some spoken languages. It is familiar to English-speakers, as the th sound in father. Its symbol in the International Phonetic Alphabet is eth, or [ð] and was taken from the Old English and Icelandic letter eth, which could stand for either a voiced or unvoiced interdental non-sibilant fricative.
The letter ⟨ð⟩ is sometimes used to represent the dental approximant, a similar sound, which no language is known to contrast with a dental non-sibilant fricative, but the approximant is more clearly written with the lowering diacritic: ⟨ð̞⟩. Very rarely used variant transcriptions of the dental approximant include ⟨ʋ̠⟩ (retracted [ʋ]), ⟨ɹ̟⟩ (advanced [ɹ]) and ⟨ɹ̪⟩ (dentalized [ɹ]). It has been proposed that either a turned ⟨ð⟩ or reversed ⟨ð⟩ be used as a dedicated symbol for the dental approximant, but despite occasional usage this has not gained general acceptance. Dental non-sibilant fricatives are often called "interdental" because they are often produced with the tongue between the upper and lower teeth (as in English), and not just against the back of the upper teeth, as they are with other dental consonants.
Features of the voiced dental non-sibilant fricative:
Its manner of articulation is fricative, which means it is produced by constricting air flow through a narrow channel at the place of articulation, causing turbulence. It does not have the grooved tongue and directed airflow, or the high frequencies, of a sibilant.