Yeísmo (Spanish pronunciation: [ʝeˈismo]) is a distinctive feature of many dialects of the Spanish language, which consists of the loss of the traditional palatal lateral approximant phoneme /ʎ/ (written ⟨ll⟩) and its merger into the phoneme /ʝ/ (written ⟨y⟩), usually realized as a palatal approximant or affricate. In other words, ⟨ll⟩ and ⟨y⟩ represent the same sound /ʝ/. The term yeísmo comes from the Spanish name of the letter ⟨y⟩ (ye). Nowadays over 90% of Spanish dialects exhibit this phonemic merger.  Similar mergers exist in other languages, such as Italian, Catalan, Portuguese or Galician, with different social considerations. Occasionally the term lleísmo (pronounced: [ʎeˈismo]) has been used to refer to the maintenance of the phonemic distinction between /ʝ/ (spelled "y") and /ʎ/ (spelled "ll").
Most dialects that merge the two sounds represented by ⟨ll⟩ and ⟨j⟩ commonly realize the remaining sound as a voiced palatal fricative [ʝ], which is similar to the ⟨y⟩ in English yellow, though it may also sound like ⟨j⟩ in English jar, especially after /n/, /l/, or at the beginning of a word. For example, relleno is pronounced [reˈʝeno] while conllevar is pronounced [koɲɟ͡ʝeˈβaɾ] or [koɲdʒeˈβaɾ]. In Spanish spoken in most of Argentina, this sound is pronounced [ʒ]; and in Buenos Aires the sound has recently been devoiced to [ʃ] among the younger population.
Extent of yeísmo and lleísmo
At present, the distinction between /ʝ/ and /ʎ/ remains in the Ecuadoran highlands, Andean Peru, Paraguay, most of Bolivia and the northeastern portions of Argentinathat border with Paraguay. The distinction is more common in areas where bilingualism with indigenous languages such as Aymara and Guaraní is common. In Spain, most of the northern half of the country and several areas in the south used to retain the distinction, butyeísmo has spread throughout the country, and the distinction is now lost in most of Spain, particularly outside of areas with linguistic contact with Catalan and Basque.
- haya ("beech tree" / "that there be") ~ halla ("s/he finds")
- cayó ("s/he fell") ~ calló ("s/he became silent")
- hoya ("pit, hole") ~ olla ("pot")
- baya ("berry") / vaya ("that he go") ~ valla ("fence")
Due to the relatively low frequency of both /ʝ/ and /ʎ/, confusion is unlikely. However, orthographic mistakes are common (for example, writing llendo instead of yendo). A similar effect took place in the local name of the island of Majorca: Mallorca is a continental Catalan hypercorrection of the earlier Maiorca.
- "La "i griega" se llamará "ye"" Cuba Debate. 2010-11-05. Retrieved 25 November 2010.
- Coloma (2011), p. 103.
- Álvarez Menendez (2005), p. 104.
- Schwegler, Kempff & Ameal-Guerra (2009), p. 399.
- Travis (2009), p. 76.
- Martínez-Celdrán, Fernández-Planas & Carrera-Sabaté (2003), p. 258.
- Lipski (1994), p. 170.
- Coloma (2011), p. 95.
- Lapesa, Rafael. "El español de América" (in Spanish). Cultural Antonio de Nebrija.
- Coloma (2011), pp. 110–111.
- Diccionari català-valencià-balear, Institut d'Estudis Catalans (look up the term "Mallorca")
- Álvarez Menendez, Alfredo I (2005), Hablar en español: la cortesía verbal, la pronunciación estándar del español, las formas de expresión oral, Universidad de Oviedo
- Coloma, German (2011), "Valoracion socioeconomica de los rasgos foneticos dialectales de la lengua espanola.", Lexis 35 (1): 91–118
- Lipski, John (1994), Latin American Spanish, New York: Longman Publishing
- Martínez-Celdrán, Eugenio; Fernández-Planas, Ana Ma.; Carrera-Sabaté, Josefina (2003), "Castilian Spanish", Journal of the International Phonetic Association 33 (2): 255–259, doi:10.1017/S0025100303001373
- Torreblanca, Máximo (1974), "Estado actual del lleísmo y de la h aspirada en el noroeste de la provincia de Toledo", Revista de dialectología y tradiciones populares 30 (1-2): 77–90
- Schwegler, Armin; Kempff, Juergen; Ameal-Guerra, Ana (2009), Fonética y fonología españolas, John Wiley & Sons, ISBN 0470421924
- Travis, Catherine E. (2009), Introducción a la lingüística hispánica, Cambridge University Press
- Pharies, David (2007). A Brief History of the Spanish Language. University of Chicago Press. ISBN 978-0-226-66683-9.