AnaMaria...tenure can´t be translated exactly, I think, but vitalicio is an adjective often used to refer to a lifetime appointment, such as that held by some judges, (or God forbid, by some war criminals who get themselves appointed for life to the Senates of their countries) which is almost the same thing. Catedrático, as the folks have told you, is a high ranking faculty member, equivalent to "university professor" at some Institutions, or the holder of an endowed "chair." Sometimes it refers to the head of a department, as the Cátedra de Filòsofía in the University of Parangaricutirimícuaro. If you give us the specific example, maybe we can be more helpful.