The article deals with the issue of the content of the so-called "secret knowledge" in the Babylonian-Assyrian esoteric commentaries on calendar months and festivals. First, the semantics of the concept of "secret knowledge" in the Sumerian and Akkadian languages is considered. Then, the ideas about the origin and the carriers of secret knowledge are studied from the point of view of the cuneiform tradition. Further, we are talking about the formulas of prohibitions on the transfer of secret knowledge to those uninitiated in it. It has been established that formulas for prohibiting the transmission of secret knowledge are found in explanatory literature, as well as in records of rituals and recipes. The article considers esoteric commentaries on calendar months and holidays, compiled in the 6th-3rd centuries BC. The secret knowledge contained in them determines the causal links between the events of the sacred calendar year. It has been established that “secret knowledge” is represented by the following types of interaction between semantic units: 1. Explanation of a word through consonant words in the languages of neighboring cultures. 2. Explanation/prediction of an event through decomposition of a word into compound words of a neighboring language. 3. Prediction of the favorableness of an action by correlating it with the calendar month and monthly ritual. In the comments, both fragments of various divinatory series and lines of literary works are involved in the explanation. We can confidently say that the main source of esoteric commentary on the calendar was the Babylonian epic of Creation “Enuma elish”, compiled in the middle of the 2nd millennium BC. The first mentions of prohibitions on the transmission of secret knowledge also date back to this time. These two facts suggest that the very tradition of esoteric commenting on the calendar and holidays dates back to the last period of the Kassite era in Babylonia (13th-11th centuries BC).