Abstract
The authors analyse Russian and Czech idioms with meaning "something unknown, secret". These idioms can have different origin: they can be connected with Grecian myths, Biblical texts, European history or they can appear in Russian or Czech.
Analysis shows, that so called international idioms can be common for all European linguagues, but also can have their national specificity. The most important thing is the idea, which we see in the base of the idioms.
Many valuable articles and books about this topic were written by Jana Skladaná. These works are quoted in the artickle.