Pronunciation of d in Spanish

The letter d has two pronunciations in Spanish. It can be a dental plosive or an interdental fricative. The two sounds are in complementary distribution. They are thus allophones of the phoneme /d/.

The dental plosive occurs word-initially and after the alveolar nasal [n] and the alveolar lateral [l]. The interdental fricative occurs intervocalically and word-finally. The intervocalic position can also extend to word boundaries. The word diferencia (difference) is pronounced with a dental plosive, but the phrase la diferencia is pronounced with an interdental fricative. The fricative also occurs after the alveolar trill [r].

The following words are pronounced with the dental plosive:

diccionario (dictionary)
diez (ten)
dos (two)
falda (skirt)
mundo (world)

The following words are pronounced with the interdental fricative:

comida (food)
izquierda (left)
libertad (liberty)
miedo (fear)
sed (thirst)

The examples illustrate that the Spanish d has two pronounciations. The interdental fricative occurs intervocalically and word-finally, and the dental plosive occurs word-initially and can also occur word-medially. The interdental fricative can be considered the result of lenition.