The Spanish variety spoken in San Sebastian is sprinkled with words of Basque origin which are often used by the speakers without awareness of the peculiar nature of such expressions. Lexical interferences slip into Spanish without the speaker placing any restrictions to a term that can bring in expresiveness or prestige, or serves to refer to an entity that simply, does not have an equivalent in Spanish, for example, ertzaintza. This study collects a corpus of such Basque lexical items, as well as an interpretation of such terminological transfer. Furthermore, words of diverse origin which are idiosincratic to the Spanish spoken in San Sebastian have also been collected