When a historian-lexicographer meets an unfamiliar word that denoted in the past any thing or concept that has long gone out of use, then to determine its meaning, he relies on the contexts containing this word. Sometimes contexts do not give an idea of ​ ​ the meaning of a word - without an accurate description of reality, its semantics cannot be determined. Numerous handwritten and published sources, extracts from which are contained in large domestic historical file cabinets, help lexicologists and lexicographers in their research. Linguistic source study is of particular importance in solving the problems of historical lexicology and lexicography.