The paper is focused on historical semantics of the term Philosophy, which we can find in Church Slavonic Vita Constantini. Semantics of the term is explained on the basis of the Byzantine sources especially the works of Maxim the Confessor and John Damascene. The definition of philosophy (Vita Constantini IV.) is reconstructed in Glagolitic original and the Greek textual equivalents of this definition are adduced. The text of John Damascene being its most probable source. In the definition, the term gnosis is explained. The formal and systematic view of philosophy and its content, as displayed in the Byzantine literature of the 7th and 8th centuries, is investigated.