The naming of UI elements where the name is a composite noun in the Qt is inconsistent. We have for instance both "radio button" and "radiobutton", "check box" and "checkbox", "tool tip" and "tooltip", "tab bar" and "tabbar".

I vaguely recall that we had some documentation style guide from back in the early aughties, but don't find it on https://wiki.qt.io/Qt_Writing_Guidelines and don't remember the details.