In every European language we find a great number of phraseological units of biblical origin, but each language has its own peculiarities in adopting these units. At the same time the text of the Bible has its own phraseological system too, which is obviously different from the systems inherited by the European languages. This approach gives us the way to obtain relevant results in diachronic research. The practical application of this method is presented in the analysis of the origin of the idiom
under the open sky
As it is generally accepted by main researchers in the field of Slavic loanwords of the Hungarian language, practically no East Slavic influence can be detected on the oldest layer of the Slavic borrowings. New etymologies established in some cases reflect East Slavic pleophony, and the analysis of well-known Slavic loanwords with TorT, TolT, TerT, TelT can give a new look at the whole body of Slavic borrowings. Pleophony seems one of the main criteria to establish an opposition between East Slavic loanwords on the one hand and South and West Slavic borrowings on the other. The material of our research requires a new classification in the corpus of Slavic loanwords in Hungarian.