Tesoro de la lengua castellana o española

The Tesoro de la lengua castellana o española (Thesaurus of Castilian or Spanish Language) is a dictionary of the Spanish language, written by Sebastián de Covarrubias in 1611.

It was the first monolingual dictionary of the Castilian (Spanish) language, with its lexicon defined in Spanish. The etymological dictionary was among the first of its type published in Europe in a vernacular language.