Use the Oxford English Dictionary (OED) to find the changes in uses of the English words. The OED tells you the part of the speech of the word, its definition, its origin, and its change in usage over time. Citing and dating the first documented use of the word in a sentence within a published work, the OED establishes when and by whom words entered into common usage and, conversely, when they became seldom used. To use the OED
When searching for historical documents, consider the terms used at the time.
For example, if you are trying to find primary sources on movies in the 1920s, they used the term “talking pictures” rather than movies. If you are trying to find articles about disabled people published in the 1970s, you might find more documents using the term of the time, “handicapped”.
Meanings change over time, and your understanding of a definition may be tainted by your modern perspective (e.g., “nationalism” or “middle class” or “capitalism”).