There is no general agreement on the terms "monolingual dictionary" and "bilingual dictionary". In the theoretical literature several different and sometimes contradicting definitions can be found. Through an analysis of different types of dictionaries, this paper shows that it is impossible to draw an exact demarcation line between monolingual and bilingual dictionaries and that the concept of bilinguality in any case is a gradual concept when it is related to dictionaries. Finally, the paper suggests that the concepts of monolingual and bilingual dictionaries are secondary aspects in terms of dictionaries and that much more emphasis should be put on the lexicographic functions.