ˈrüsə̇nz- noun
Usage: usually capitalized R
Etymology: after François-Zacharie Roussin died 1894 French chemist
: any of two series of alkali metal salts that are nitrosyl and sulfur complexes of iron:
a. : a red unstable salt having the general formula M[Fe(NO) 2 S] and obtainable by reaction of nitric oxide with ferrous sulfide
b. : a black more stable salt having the general formula M[Fe 4 (NO) 7 S 3 ] and obtainable (as by treatment with alkali) from a red salt