The present study examines the representation of Arabic and Hebrew in Covarrubias’s Tesoro de la lengua castellana o española from a comparative perspective. Analyzing the lexicographer’s ideological and meta-linguistic discourse, I reconstruct his postulates regarding the respective histories of Arabic and Hebrew, their interrelationship, and place in the history of Spanish. In light of these postulates, and taking into account the lexicographer’s access to knowledge, sources, and informants, I examine some of his etymological practices, focusing on his attempts to use (...) grammatical and lexical knowledge of Hebrew to illuminate Arabic etymologies of Spanish words. Combining the ideological and technical levels of the text, I reflect on the interplay of knowledge and ignorance in Covarrubias’s treatment of Semitic languages. (shrink)