The article discusses the main stages of analysing the agnonym kurtina ( curtain wall/clump). An agnonymis a lexical unit unfamiliar to native speakers. Words from Russian classical literature often become agnonymsfor modern youth who just skip unfamiliar lexemes while reading texts. Thus, such lexical units do not enrich schoolchildren’s vocabulary and remain incomprehensible and unrecognis able in other contexts. Drawing on the example of working with the agnonym kurtina when studying other unknown/forgotten units, the authors suggest using a linguistic questionnaire to identify unfamiliar words. Additionally, we recommend employing dictionary data and contexts obtained from the Russian National Corpus in order to trace the semantic transformation of these lexemes. While working with the word kurtina in Russian language classes, we were able to assume that the lexical status of this word changed at the beginning of the 21st century. One of its meanings has ceased to be obsolete passing into the layer of general professional vocabulary.