The normative space of legal discourse does not only contain norms of various types and functions - regulatory and constitutive, formal and non-formal - but also implicates general value-based benchmarks of both social behavior of society in general and the representatives of political and state power and their "way of thinking". The article considers the correlation between the etymology of the English word, used in the text of legal discourse, and the cognitive reconstruction of the meanings of the concept «reasonable authority» on the example of Family Procedure Rules used in England and Wales. Etymological memory of a word is viewed upon in this study as a «mobile determiner» of the context, able to modify the conception of the UK judiciary. The etymology of a word should reveal the deep semantics of lexical units, uncover inferential characteristics and show the connotations of the word.