This article addresses universal laws of the functioning of open systems involved in myth-oriented semiosis, categorisation and world-modelling. The paper focuses on isomorphic regularities occurring in irrational rationalisation and respective verbal phenomena. The outlined systemic and inter-systemic interactions are interpreted from the standpoint of M-logic methodology, semiotics, cognitive linguistics and cultural studies. The paper suggests formalised notations for logical construals, and demonstrates the cognitive premises of myth-oriented designations and the etymological reconstruction of a basic operator’s content.