Chisels with a rectangular cross section are called firmer chisels. I learned that’s because they were firmer than a bevlel edge chisel, but that’s not the etymology.
The OED says it’s from the French foumer ( to form) and Joseph Moxon called them former chisels In a 1670 pamphlet. A hundred years later Eave’s woodworking dictionary called them “ former or firmer chisels. “ they are generally used for work that required more force than a bevel edge chisel, and they were more common than other types.
But that distinction has gotten muddier over time. Some manufacturers ( Hirsh, Marples) still call rectangular cross section chisels firmers , but other manufacturers call their socket chisels firmers just to keep us confused. And others call them mortise chisels, but they aren’t as stout as pigstickers.