N-gram viewer lets you check the usage frequency of written terms (relative abundance, i.e. number of instances of a given n-gram or string of characters in a particular year divided by total number of words used in a sample of books published in that year, with a single word being a one-gram) found in millions of digitized books, in several languages, during a specified time period.
Thus you can observe grammatical changes over centuries: for example, the gradual movement of a verb from commonly having an irregular conjugation (e.g. burnt as past tense of burn) to a regular one (burned).
You can also see how historical-political change is reflected in the written lexicon.
No need for use of a term specifying a movement or ideology that is defeated, vanished or as-yet undreamt of (or is that undreamed?). On the other hand, being talk of the town may be a sign of social ascendancy.
Observe (o tempora o mores!) the following plots in English, French and Spanish:
Usage of the German Sozialismus is not comparable over the same timescale, for obvious reasons; but restricted to post-WW2 years it exhibits the same general trend, with use of the word peaking around 1980. Same for Kommunismus.
The emergence of Minsky’s money-manager capitalism also shows up:
How ‘traditional’ is the owner, and how universal is property?
Pop-academia-derived buzzwords like paradigm show up: