Free online dictionary featuring translations in English-Spanish, Spanish-English Also provides other useful tools like conjugation and how to use words in context.
A monolingual Spanish dictionary, good for advanced learners, from the Royal Spanish Academy (Real Academia Española or RAE), which is the official royal institution responsible for regulating the Spanish language.
An online directory of centuries-old books and documents on the Spanish language, including dictionaries, dialogues, grammatical lessons, and historical books on Spanish linguistics
Diccionario de la lengua española (Real Academia Española : Online) by