One unusual feature of Spanish etymology is the way in which the liquids/r/ and /l/ have sometimes replaced each other in words derived from Latin, French and other sources. For example, Spanish milagro, "miracle", is derived from Latin miraculum. More rarely, this process has involved consonants like /d/ and /n/ (as in alma, from Latin anima). Here is an incomplete list of such words:
Documents from as early as the 15th century show occasional evidence of sporadic confusion between the phoneme /ʝ/ (generally spelled ⟨y⟩) and the palatal lateral /ʎ/ (spelled ⟨ll⟩). The distinction is maintained in spelling, but in most dialects of Modern Spanish, the two have merged into the same, non-lateral palatal sound. Thus, for example, most Spanish-speakers have the same pronunciation for haya (from the verb haber) as for halla (from hallar). The phonemic merger is called yeísmo, based on one name for the letter ⟨y⟩.
Yeismo is a trait of the Andalusian dialect, among others. Since more than half of the early settlers of Spanish America came from Andalusia, most Spanish-speaking regions of the Americas have yeísmo, but there are pockets in which the sounds are still distinguished. Native-speakers of neighboring languages, such as Galician, Astur-Leonese, Basque, Aragonese, Occitan and Catalan, usually do not feature yeísmo in their Spanish since those languages retain the /ʎ/ phoneme.
A related trait that has also been documented sporadically for several hundred years is rehilamiento (literally "whizzing"), the pronunciation of /ʝ/ as a sibilant fricative [ʒ] or even an affricate[dʒ], which is common among non-native Spanish speakers as well. The current pronunciation varies greatly depending on the geographical dialect and sociolect (with [dʒ], especially, stigmatized except at the beginning of a word). Rioplatense Spanish (of Argentina and Uruguay) is particularly known for the pronunciation [ʒ] of both /ʝ/ and original /ʎ/. A further development, the unvoiced pronunciation [ʃ], during the second half of the twentieth century came to characterize the speech of "most younger residents of Buenos Aires" and continues to spread throughout Argentina.
Boyd-Bowman, Peter (1964), Índice geobiográfico de cuarenta mil pobladores españoles de América en el siglo XVI (Vol. I), Bogotá: Instituto Caro y Cuervo
Corominas, Joan (1973), Breve diccionario etimológico de la lengua castellana, Madrid: Gredos
Cravens, Thomas D. (2002), Comparative Historical Dialectology: Italo-Romance clues to Hispano-Romance sound change, Amsterdam: John Benjamins
Hammond, Robert M. (2001), The Sounds of Spanish: Analysis and Application (with Special Reference to American English), Somerville, Massachusetts: Cascadilla Press, ISBN1-57473-018-5
Lapesa, Rafael (1981) [1942], Historia de la lengua española (9th ed.), Madrid: Gredos, ISBN84-249-0072-3
Lathrop, Thomas A. (2003), The Evolution of Spanish, Newark, Delaware: Juan de la Cuesta, ISBN1-58977-014-5
Lipski, John M. (1994), Latin American Spanish, London: Longman
Navarro Tomás, Tomás (1982) [1918], Manual de pronunciación española (21st ed.), Madrid: Concejo Superior de Investigaciones Científicas, ISBN84-00-03462-7
Walsh, Thomas J. (1991), "The Demise of Lenition as a Productive Phonological Process in Hispano-Romance", in Harris-Northall, Ray; Cravens, Thomas D. (eds.), Linguistic Studies in Medieval Spanish, Madison: Hispanic Seminary of Medieval Studies, pp. 149–163