sesquicarbonate

noun

ses·​qui·​car·​bon·​ate ˌse-skwi-ˈkär-bə-ˌnāt 

-nət

: a salt (such as Na₂CO₃·NaHCO₃·2H₂O) that is neither a simple normal carbonate nor a simple bicarbonate but often a combination of the two

Word History

First Known Use

1825, in the meaning defined above