Abstract
The article deals with definition problems of the archaism and the historism. First we compare how monolingual dictionaries define their meaning, then a choice of Czech and Slovak professional literature is presented, and finally lexicographic principles of the treatment of diachronic marked words are discussed.
For distinguishing of archaisms and historisms the following criteria appear central: the cause of obsolescence of lexical units, the possibility of making synonyms and the use in different types of texts. In relation to old expressions there were found terminological diversities: old expressions can be understood as hyperonyms to archaisms and historisms, as synonyms for archaisms, or they can be distinguished from archaisms by their function and by the degree of obsolescence.