History of the Term "Conspiracy Theory" The term "conspiracy theory" is used to describe any theory that attempts to characterize observed events as the result of some secret conspiracy. The term is often used dismissively, implying that the theory is implausible. Although conspiracy theories (particularly aimed at Jews and Bankers) date back hundreds of years, the earliest usage of "conspiracy theory" do not always have this connotation, although the theories are quite often dismissed in other ways. Usually it's simply a way of identifying the theory from other theories - as in "the theory that happens to have a conspiracy" The first usage I could find was from 1870, The Journal of mental science: Volume 16 - Page 141 1890 - Some kind of political conspiracy, mostly ridiculed http://books.google.com/books?id=ziIgAQAAMAAJ&dq="conspiracy theory"&pg=PA608-IA7#v=onepage&q="conspiracy theory"&f=false Here from a review of theories about the causes of the secession of the South, 1895. http://books.google.com/books?id=f9ghAQAAMAAJ&dq="conspiracy theory"&pg=PA394#v=onepage&q="conspiracy theory"&f=false Also on the same topic 1895 http://books.google.com/books?id=GkIxAQAAMAAJ&dq="conspiracy theory"&pg=RA16-PA27#v=onepage&q="conspiracy theory"&f=false Given the multiple usages on the subject of succession, it seems plausible that this is a key point in the evolution of the phrase. It shifts from simple incidental use in language to referring to a specific thing. From "that theory which has a conspiracy" to "the theory that we call conspiracy theory" 1899, this is more like it, from an article discussing various conspiracy theories regarding South Africa. And an early debunking: http://books.google.com/books?id=cHdNAAAAYAAJ&dq="conspiracy theory"&pg=PA227#v=onepage&q="conspiracy theory"&f=false Here it's seeming to move towards its current use with an implied "far-fetched" prepended. Some people get a bit upset when you use the term "conspiracy theory", so I think it's good to be clear on what you mean. One might say "I know it when I see it", like say 9/11 no-plane theories, or fake moon-landing theories. I think Aaronovitch has something right here: Aaronovitch, David (2010-01-19). Voodoo Histories: The Role of the Conspiracy Theory in Shaping Modern History (pp. 5-6). Penguin Group. Kindle Edition.