I think it’s interesting that Harrow’s rib corset is actually described by name only twice – once as a corset, once as a corselet.
Ianthe calls it a corset. Ianthe, who heralds from the fashion capitol of Dominicus, refers to it as an accessory.
Gideon calls it a corselet. Gideon, who’s fought Harrow a thousand times, who knows how deadly even an inch of bone can be if within theorum distance of the Reverend Daughter, who’s spent her entire life learning the blade, refers to it as armor.