In the history of cryptography, the Nihilist cipher is a manually operated symmetric encryption cipher originally used by Russian Nihilists in the 1880s to organize terrorism against the tsarist regime. The term is sometimes extended to several improved algorithms used much later for communication by the First Chief Directorate with its spies.

More information, including examples, on the Wikipedia page [1].

Wilfrid Voynich, Stepniak and others in the Society of Friends of Russian Freedom may have been familiar with the cipher.