ferrocyanide
noun
fer·ro·cy·a·nide ˌfer-ō-ˈsī-ə-ˌnīd 
1
: the tetravalent anion Fe(CN)64−
2
: a compound containing the ferrocyanide anion
especially : the salt K4Fe(CN)6 used in making blue pigments (such as Prussian blue)
Example Sentences
Recent Examples on the Web The ensuing reaction created a distinctive blue-hued iron ferrocyanide and eventually came to be called Prussian blue (or Berlin blue). 
Jennifer Ouellette, Ars Technica, 20 June 2022 So then, in certain kinds of lakes, ferrocyanide can accumulate over time. Quanta Magazine, 1 June 2022 Riepenhoff got the idea three years ago while studying cyanotypes, an old photo technique that involves placing objects on paper coated with iron and potassium ferrocyanide. Laura Mallonee, WIRED, 30 Aug. 2016
Jennifer Ouellette, Ars Technica, 20 June 2022 So then, in certain kinds of lakes, ferrocyanide can accumulate over time. Quanta Magazine, 1 June 2022 Riepenhoff got the idea three years ago while studying cyanotypes, an old photo technique that involves placing objects on paper coated with iron and potassium ferrocyanide. Laura Mallonee, WIRED, 30 Aug. 2016 Word History
First Known Use
1825, in the meaning defined at sense 1
Medical Definition
ferrocyanide
noun
fer·ro·cy·a·nide ˌfer-ō-ˈsī-ə-ˌnīd
1
: the tetravalent anion Fe(CN)64−
2
: a compound containing the ferrocyanide anion
especially : the salt K4Fe(CN)6 used in making blue pigments (as Prussian blue)