The article analyzes the use of obscure Slavic terms (calcifi ed from the ancient Greek compound words εὐκρασία ‘good mixture’ and εὔκρατος ‘well mixed’, respectively) in Church Slavonic texts. The considered fragments of Church Slavonic texts (primarily taken from modern Church Slavonic worship) with the lexemes under study are compared with their Greek originals (if any are available) and with the Greek dictionaries information. Examples of these ancient Greek lexemes having the same meanings in classical texts are given with the accepted literary translation into Russian or English for comparison. It is clarifi ed how the church texts refl ect the meanings of these terms (‘right mixture of the elements in the human body’, ‘moderate, favorable force for a human’, ‘good mixture of heat and cold, i.e. the right temperature’), arising from those that have existed since antiquity natural-philosophical ideas about the nature of the world and man. The article also shows how in the era of wide dissemination of the new ideas about nature and man (the miasmatic theory of diseases) in Russia incomprehensible expressions, such as “blagorastvoreniye vozdukhov” were reinterpreted by listeners who were not skilled in the classical languages, as ‘cleanliness, good smell and non-sickness of the air’.