The reason why they share the same prefix is because it is being firstly obtained by the heating of the pigment known as Prussian blue.
|Prussian blue. Source: Wikipedia|
Prussian blue is a dark blue pigment with the idealized chemical formula Fe 7(CN) 18. To better understand the binding situation in this complex compound the formula can also be written as Fe 4[Fe(CN) 6] 3 · xH 2O. It is the first synthetic dye. It also called Berlin Blue or Persian/Paris Blue. It is the traditional "blue" in blueprints.
Prussian blue can be use to treat thallium poisoning. It was synthesized by the paint maker Johann Jacob Diesbach in 1706.
Because cyanide was obtained from Prussian blue at first, it was named cyanide as a reference of blue. The Greek for dark blue is kyanos.
Wikipedia. Cyanide - Nomenclature and Etymology.